the learning never stops!

  Gray Areas  


When we have incomplete knowledge about an upcoming decision we tend to say it is an issue mired in a gray area and therefore open to our personal judgement. That kind of latitude leads to rule bending and more times than not, the wrong answer. A better way to respond to a question from the gray area is with the answer: it depends.

After you say "it depends" the natural follow up question is, "it depends on what?"

  • Rules, regulations, manuals, handbooks; there might be something out there and not knowing it may not be a sufficient excuse if things get ugly.
  • Physics; if you can't find it in the laws of man, it could be that it is a law of nature.
  • History; it may be helpful to know what there is in accident databases or just pilot reports from those who came before you.

Seeing through the gray of an issue is more of a skill than a checklist of sequential steps. It is a talent you can develop but it takes practice. Fortunately, you don't have to learn from your own mistakes. You can think the problems through ahead of time and it may help to examine a case study or two.



Cartoon: Minimum fuel, from Chris Manno.

  1. Currency (landing and takeoff) —or— "An SIC isn't the PIC"
  2. Minimum Fuel —or— "A little extra for the kids"
  3. Circling —or— "A modified VFR pattern"
  4. Conditions Conducive to Icing Accumulation —or— "It isn't sticking"
  5. Grooved Runways —or— "It's kinda dry"
  6. Wind Shear —or— "It's little gusty"
  7. 135 En Route, Start / End 91 Duty Limits —or— "No pax / no worries"
  8. Departure Obstacle Avoidance —or— "What if we don't lose an engine, we're okay, right?"

Currency (landing and takeoff) —or— "An SIC isn't the PIC"

To half of you, the following statement will seem obviously true. To the other half, the following statement will seem obviously absurd. So that makes it a perfect gray area.

Hypothesis: Takeoff and landing currency rules restricts a pilot from acting as a pilot in command of an aircraft carrying passengers unless he or she has met the recent flight experience rules in 14 CFR 61.57. There are no such restrictions imposed on a second in command, so an SIC may regain currency while flying with passengers on board so long as the PIC is current.

When I first heard this I was coming from 20 years of military flying and thought the civilian side of the fence had gone nuts. But a careful reading of the rules would lead you to believe perhaps there was something to this . . .

[14 CFR §1] Pilot in command means the person who:

(1) Has final authority and responsibility for the operation and safety of the flight;

(2) Has been designated as pilot in command before or during the flight; and

(3) Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight.

[14 CFR §61, ¶61.57] Recent flight experience: Pilot in Command.

(a) General experience. (1) Except as provided in paragraph (e) of this section, no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days, and—

(i) The person acted as the sole manipulator of the flight controls; and

(ii) The required takeoffs and landings were performed in an aircraft of the same category, class, and type (if a type rating is required), and, if the aircraft to be flown is an airplane with a tail wheel, the takeoffs and landings must have been made to a full stop in an airplane with a tail wheel.

(2) For the purpose of meeting the requirements of paragraph (a)(1) of this section, a person may act as a pilot in command of an aircraft under day VFR or day IFR, provided no persons or property are carried on board the aircraft, other than those necessary for the conduct of the flight.

(3) The takeoffs and landings required by paragraph (a)(1) of this section may be accomplished in a flight simulator or flight training device that is—

(i) Approved by the Administrator for landings; and

(ii) Used in accordance with an approved course conducted by a training center certificated under part 142 of this chapter.

But still, this is nuts! So when I was a check airman with TAG Aviation USA, we asked our POI who told us we were nuts. No, he said, any pilot is restricted from taking off or landing with passengers unless current. The rule doesn't say that explicitly, but that's what it means. That was back in 2005. We looked at it again in 2016. Our representative, whom I shall call "us," was flying as an airline passenger with two FAA inspectors to a conference of some sort. I shall call them the "Feds." Here is the conversation:

Feds: "Yup, all he needs is 3 takeoffs and landings for Part 91."

Us: "With passengers?"

Feds: "Only the PIC can be the sole manipulator of the controls."

Us: "Fully half of Delta's landings today will be made with the SIC as the sole manipulator."

Feds: Silence.

Feds: Looking at each other in some sort of secret code.

Us: "You guys have both flown 121, does IOE ever happen at night?"

Feds: "Yes."

Us: "So if he's new to the airplane and new to the seat...."

Feds: "Legally you maybe right but the PIC needs to be ready to explain to the judge how he ended up in the grass letting the SIC land."

These two inspectors had clearly been in the jump seat with an SIC acting as the sole manipulator of the controls but had never considered this gray area. And these two inspectors were among the good ones. My recommendation: treat the term PIC to mean pilot when it comes to recency of experience. You should not be regaining your currency with passengers on board, even if the other guy is signing for the jet.

Minimum Fuel —or— "A little extra for the kids"

When we started our flying careers we may have liked to say "You can never have too much fuel." Then, whenever we made the step up to turbines, we would add, ". . . unless you are on fire." If you fly commercially (14 CFR 135, for example), you would have to add, ". . . unless it puts you overweight at your destination." Then when you started crossing oceans for a living, you needed to add, ". . . unless it makes you too heavy at level off to maintain Mach." So that takes care of the maximum. What about the minimum?

Regulations (14 CFR 91, 14 CFR 135, etc.)


Figure: Departure / Destination / Alternate fuel minimums, from Eddie's notes.

[14 CFR 91, §91.151] Fuel Requirements for flight in VFR conditions

(a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed—

(1) During the day, to fly after that for at least 30 minutes; or

(2) At night, to fly after that for at least 45 minutes.

[14 CFR 91, §91.167] Fuel requirements for flight in IFR conditions

(a) No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to—

(1) Complete the flight to the first airport of intended landing;

(2) Except as provided in paragraph (b) of this section, fly from that airport to the alternate airport; and

(3) Fly after that for 45 minutes at normal cruising speed or, for helicopters, fly after that for 30 minutes at normal cruising speed.

(b) Paragraph (a)(2) of this section does not apply if:

(1) Part 97 of this chapter prescribes a standard instrument approach procedure to, or a special instrument approach procedure has been issued by the Administrator to the operator for, the first airport of intended landing; and

(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:

(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.

You can make this a lot simpler if you agree you should always plan for IFR operations with an alternate. If you do that, your minimum regulatory fuel becomes enough to fly the trip, shoot an approach, climb as needed to make your alternate, cruise to the alternate, shoot the next approach, land, and carry another 45 minutes of fuel based on the cruise altitude you used to get to your alternate.

More about this: Minimums.

Rules (Company-specified)

Your company can simplify things further by requiring a higher minimum that makes getting to the regulatory limit easy. Be sure to check your Operations Specifications, if you have them, for further guidance. Here's what we have at Incognito Air:

[Incognito Air Operations Manual, §] Minimum Fuel. Aircraft should be on the ground with not less than 1 hour of fuel remaining. Landing with less than 45 minutes fuel remaining requires a report to the Flight Department Manager of circumstances surrounding the incident.

Physics (Aircraft gauge tolerances, flight planning software errors)


Figure: KBED to KBOS divert fuel in a G450 according to GDC, from Eddie's notes.

If you are flying an aircraft with analog gauges and rudimentary probes you may want to increase your minimums to account for fuel gauge tolerances. The older Boeing 707's that I flew had tolerances equal to 10% of the gauge's total indication, meaning a tank could be at 2,400 lbs and actually be empty. Most modern gauges are better but few manufacturers publish tolerances. Gulfstream is quiet on this subject except for those airplanes not originally designed in Savannah. The G100, for example, has fuel gauges with an accuracy of 2% of the current indication plus 0.75% of the full scale value.

More about this: G450 Fuel Quantity.


Figure: KBED to KBOS full flight plan fuel in a G450, from Eddie's notes.

Another issue involves most flight planning software. GDC, for example, says we can divert from Hanscom Field in Bedford, MA to Logan IAP in Boston, MA using just 328 pounds of fuel. But this is based on a direct flight with no vectors or other delays. If you cannot input an expected divert flight plan, you should have an idea how much fuel it will really take. In the case of our KBED to KBOS divert, running such a flight plan reveals it will take at least three times as much fuel.

History (Case Studies)

You should always have an idea of how much fuel you start with, how much you've asked to have added, and how much you should have ended up with. If these don't add up, you need to investigate.

More about this: Executive Airlines N16EJ.

You cannot assume the fueler knows what he is doing and you must be especially alert when there are issues of gallons to liters to pounds to kilograms involved.

More about this: Air Canada 143.

When things start to go south on you, you must immediately and aggressively point the airplane to someplace to land. If Air Traffic Control doesn't understand, be aggressive with your language. "I am declaring an emergency," should do it. But if that doesn't work try "I am minutes away from becoming a glider, if I don't get priority somebody is going to die."

More about this: Avianca 52.

Minimum fuel without gray areas

Your minimum fuel prior to takeoff, en route, and when deciding whether or not to divert should not be a gray area. At most, you can temper the answer "How much fuel do you want" with "It depends" so long as you know what it depends on. Here is my thought process and the answers I've come up with for our G450. Your thought process and answers, of course, can be different. But you should think this through before you contemplate defying gravity in that airplane of yours.

  1. Minimum fuel to fly — You need to make it to your destination under the expected weather conditions (winds, etc.) plus another 30 minutes (day) or 45 minutes (night). We simplify this by using 45 minutes, day or night. We also consider a fuel burn at our maximum landing weight of 4,000 PPH, so 45 minutes means our minimum fuel to fly is the planned en route fuel plus 3,000 pounds.
  2. Minimum fuel to fly with an alternate required — You need to add the fuel it would take to go missed approach at your planned destination, climb to the appropriate altitude, and then shoot an approach to landing at your alternate. We add the alternate to our flight plan but apply a common sense check to that. We know that both our domestic and international planning services do not realistically consider the climb and en route portions of the divert when the airports are close together. For that reason we consider a minimum of 1,000 pounds to divert. That means our minimum fuel to dispatch when an alternate is required becomes the planned burn plus 4,000 pounds.
  3. Gauge tolerances — You need to consider the accuracy of your gauges and add any necessary factor to your previously computed minimums. Our G450 fuel system is considered accurate enough (around plus or minus 200 lbs per tank) that we do not consider this necessary.
  4. Minimum fuel en route — You need to make a decision before you fly on how low you are going to allow your expected fuel upon landing before you will decide to stop early for fuel. If winds or ATC vectors make landing with your decided en route minimum questionable, you can then dispassionately decide it is time to look for fuel stop. We have decided our number is the 45 minutes of fuel figure, 3,000 pounds. If circumstances drive our expected landing fuel below 3,000 pounds, we start looking for places to land.
  5. Minimum fuel after going missed approach — If you are unable to land and end up shooting multiple approaches or end up in a holding pattern, you must have a fuel quantity in mind where you will go to Plan B. Plan B can be choosing another alternate (still shooting for the minimum number) or declaring an emergency if that will put you on the ground before going below your minimums. Here again we have decided our number is 3,000 pounds.

I know other G450 operators have numbers higher and lower than our 4,000 pounds prior to takeoff and 3,000 pounds en route. That is fine, but you need to have your numbers picked before the flight is even scheduled to remove all emotion and temptation to adjust these when the pressure is on. That is the only way to remove the gray from these decisions.

Circling —or— "A modified VFR pattern"


Figure: KTEB ILS to runway 6, circle to runway 1, versus the airport traffic area, from Eddie's notes.

There are a few places in the country where we are instructed to shoot an approach and "circle" to another runway with specific or implied instructions to deviate from circling procedures. When landing on runway 01 at Teterboro, for example, the explicit instructions are "cleared the ILS runway 6, circle to land runway 1, start your circle at TORBY." Left unsaid is the fact the TORBY is 3.8 nm from the runway and you are not to overfly Giant stadium.

More about how this is done: Teterboro.

Is this an IFR circling approach? If so, are we violating the authorized circling radii for our aircraft which is 1.7 nm (Category C) or 2.3 nm (Category D) when we commence circling at Torby? Giant Stadium poses another problem, in that shooting to turn inside of the stadium precludes a stabilized approach while shooting to turn outside also exceeds authorized circling radii.

Regulations (14 CFR 91, 14 CFR 135, etc.)

[FAA Pilot/Controller Glossary]

  • CIRCLE-TO-LAND MANEUVER− A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straight-in landing from an instrument approach is not possible or is not desirable. At tower controlled airports, this maneuver is made only after ATC authorization has been obtained and the pilot has established required visual reference to the airport.
  • CIRCLE TO RUNWAY (RUNWAY NUMBER)− Used by ATC to inform the pilot that he/she must circle to land because the runway in use is other than the runway aligned with the instrument approach procedure. When the direction of the circling maneuver in relation to the airport/runway is required, the controller will state the direction (eight cardinal compass points) and specify a left or right downwind or base leg as appropriate; e.g., "Cleared VOR Runway Three Six Approach circle to Runway Two Two," or "Circle northwest of the airport for a right downwind to Runway Two Two."

[Aeronautical Information Manual, ¶3-2-􏰀5.a.] Class D Airspace. Generally, that airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower. The configuration of each Class D airspace area is individually tailored and when instrument procedures are published, the airspace will normally be designed to contain the procedures.

[Aeronautical Information Manual, ¶5-4-3.q.] Visual Approach. A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the airport. The pilot must have either the airport or the preceding identified aircraft in sight. This approach must be authorized and controlled by the appropriate air traffic control facility. Reported weather at the airport must have a ceiling at or above 1,000 feet and visibility 3 miles or greater. ATC may authorize this type approach when it will be operationally beneficial. Visual approaches are an IFR procedure conducted under IFR in visual meteorological conditions. Cloud clearance requirements of 14 CFR Section 91.155 are not applicable, unless required by operation specifications.

A tower can clear an aircraft for a visual approach using the terminology "circle to runway XX" just as a way of communicating how they want the aircraft to maneuver. In the Teterboro example, the tower often adds the stipulation that the circle should commence at TORBY. Tower owns the airspace and is authorizing you to use that airspace to fly the visual approach. You are not constrained by the TERPS circling approach radii.

Rules (Company-specified)

Your company may specify when you may fly a circling or a visual approach, if at all. I've heard, for example, that Southwest Airlines prohibited circling approaches, period. I spent the night at the same hotel they frequented near Chicago Midway and asked them how they were able to accept "Cleared ILS 31 center, circle to 22 left" given that policy. I was told they considered those instructions to be a "modified visual approach" and that is true enough. Southwest, to its credit, got an instrument approach to runway 22 left to make the entire issue moot.

More about this: Chicago Midway.


The odds are stacked against you whenever you circle at minimums and whenever you can widen your margin, you should.

More about this: (U.S.) Circling Approach Visibility Minimums (Are Too Low!).

History (Case Studies)

A circling approach at minimums maybe the most dangerous thing you do in an airplane on a routine basis, but recognizing this fact helps you to focus on the task at hand. When tower or you improvise a circling / visual approach you may not give the procedure the necessary planning and caution. Teterboro will announce the ILS runway 6, circle to 1 on the ATIS, for example. That is your cue to examine the obstacles, consider your turn radius, and the need for a stabilized approach on roll out. An ad hoc approach to this situation can end badly.

Examples: Air Blue ABQ 202, and Air China 129.

Visual approaches without gray areas

An approach to circle to a runway is a specific instruction with minimum visibilities and maximum authorized radii. When in visual conditions and given instructions to circle to a runway you are more than likely being issued clearance to fly a visual approach. When in doubt, ask. "Please confirm this is a visual approach and we are not required to remain within 1.7 nautical miles" may get a laugh or a condescending answer, but it will remove all doubt.

I've taken to diagramming circling and visual approaches ahead of time to help remove the surprise factor.

For example (KJFK, KMEM, KDW): Circling Approaches / Examples.

Conditions Conducive to Icing Accumulation —or— "It isn't sticking"


Photo: Eddie Likes Glycol

Regulations (14 CFR 91, 14 CFR 135, etc.)

So let's say you are a true believer that you must conduct a pretakeoff contamination check within 5 minutes before beginning takeoff when the conditions are conducive to icing accumulation. When are conditions conducive to icing accumulation? Is it sticking? No? Will it stick later as you taxi out and the temperature of the wing melts it? Or what about the winds circulating about?

See Cold Weather Operations.

I flew for a few years from an airport without deice capability and had to play the game, "When it's very cold and the snow is dry, open the hangar doors and cold soak the aircraft; when it's just above freezing and the ice is melting, heat up the hangar so the aircraft is warm and whatever hits the aircraft will melt." To which I said, "nuts." Well it's a gray area. Or is it?

[Advisory Circular 20-117, Appendix 3, ¶2.] Conditions conducive to aircraft icing.

b. Aircraft on the ground, during ground storage or ground operations, are susceptible to many of the conditions that can be encountered in flight in addition to conditions peculiar to ground operations. These include:

  1. Supercooled ground fog and ice clouds.
  2. Operation on ramps, taxiways, and runways containing moisture, slush, or snow.
  3. Blown snow from snow drifts, other aircraft, buildings, or other ground structures.
  4. Snow blown by ambient winds, or other aircraft, or ground support equipment.
  5. Recirculated snow made airborne by engine, propeller, or rotor wash. Operation of jet engines in reverse thrust, reverse pitch propellers, and helicopter rotor blades are common causes of snow recirculation.
  6. Conditions of high relative humidity that may produce frost formations on aircraft surfaces having a temperature at or below the frost point.

[ICAO Doc 9640, Chapter 3]

3.1 Many atmospheric and ambient conditions can cause aeroplane icing on the ground. The principal conditions are frost, snow, freezing fog, freezing drizzle, freezing rain, and rain, drizzle, fog or high humidity combined with the cold-soak effect. The latter type of icing can occur at ambient temperatures well above the freezing point. It is also important to understand that mixed and changing atmospheric conditions can overlap during aeroplane operations on the ground, requiring constant vigilance by both flight and ground crews. Clear ice or failed anti-icing fluid can be very difficult to identify.

3.2 Other conditions that are conducive to icing contamination on aeroplane surfaces are:

a) operations on ramps, taxiways and runways contaminated by water, slush or snow. These substances may be deposited on aeroplane surfaces by wind, aeroplane operations, jet blast, or ground support equipment; and

b) warm aeroplane surfaces exposed to frozen precipitation during below-freezing conditions. The warm aeroplane surfaces may cause melting and refreezing of the precipitation.

3.3 In many cases, de-icing/anti-icing procedures may be ineffective in providing sufficient protection for continued operations. This can occur when there is freezing rain, freezing drizzle, heavy snow, or any condition where high water content is present in freezing precipitation.

3.4 At very low ambient temperatures (below approximately –30°C), some heated Type I fluids are no longer effective, and other methods of frozen contamination removal must be used.

Rules (Company-specified)

This discussion changes if you are operating under 14 CFR 121 or 14 CFR 135 with an approved deicing program and training in accordance with 14 CFR 121.629.

See: Cold Weather Operations.

Physics (And a case study)

Some aircraft are more sensitive to ice accumulation than others. Where one airplane can takeoff with a sheet of ice over every surface, others may be made unflyable with a dusting of snow. Your lot in life is made worse by those that came before you and decided to fly. "Well if Captain Blow could handle this, why can't you?"

There is no doubt some aircraft are ice intolerant and others can take a little. In either case, accumulation on one wing and not the other can render any aircraft unable to remain right-side up.

For example: CL-604 EGBB Birmingham (De-ice).

History (And another case study)

The "clean aircraft concept" has been around since the 1950's but every few years we find another example of somebody trying to widen the definition of exactly what that means. When conditions are conducive to the accumulation of airframe contamination your options narrow. If you have an approved de-icing program you have a hold over table to consult. Otherwise, you have a pretakeoff inspection to conduct. If you operating under 14 CFR 135, chances are you do not have an approved deicing program. If you are operating under 14 CFR 91, there is no doubt about it: you do not have an approved deicing program.

Perhaps the most egregious case was that of Air Florida 90.

Determining conditions conducive to icing accumulation without gray areas

Generally speaking, if it is falling from the sky at or near a frozen state it has the potential to stick to your aircraft. Even fog and humidity has the potential to change the smooth skin of your air foil to sandpaper. About the only exception to the falling from the sky scenario is very cold light snow in very cold temperatures, but even that can be a problem if the aircraft is warm. The best way to remove any gray from your go / no go decision is to get out of the airplane within five minutes of takeoff, run your hand down parts of the wing, and check.

Grooved Runways —or— "It's kinda dry"

Very few airplanes have flight test derived takeoff and landing data for wet runways; the numbers in the book are often just a canned factor added to the dry data. Our real world experience may tell us we can do better than what our charts are telling us, especially when it comes to operating on grooved runways. If your dry data says you can stop the airplane in 2,000 feet and the wet data says 2,300 feet, we know the book is just adding 15%. In some airplanes that 15% is just right. Now add to this a grooved runway and you have some decisions to make. Will the airplane stop in 2,300 feet like the book says, or 2,000 feet as if the runway were dry? Ah, that could be a gray area. Or is it?

Regulations (14 CFR 91, 14 CFR 135, etc.)

The FAA says manufacturers can make allowances for grooved runways, but they don't have to.

More about this: Grooved Runways.

[14 CFR 25 §25.105(c)(1)(ii)] The takeoff data must be based on . . . At the option of the applicant, grooved or porous friction course wet, hard-surfaced runways.

[14 CFR 25 §25.109(d)] Accelerate-stop distance. . . . At the option of the applicant, a higher wet runway braking coefficient of friction may be used for runway surfaces that have been grooved or treated with a porous friction course material.

[14 CFR 25 §25.1533(3)] Additionally, at the option of the applicant, wet runway takeoff distances may be established for runway surfaces that have been grooved or treated with a porous friction course, and may be approved for use on runways where such surfaces have been designed constructed, and maintained in a manner acceptable to the Administrator.

Rules (Aircraft-specific)

Your aircraft manufacturer may provide a factor that considers grooved runways, may disallow it, may be silent on the issue, or may have a nebulous statement that leaves you guessing. In the case of most Gulfstreams, the data in the charts does not consider grooved runways and a hard to find statement leads you to believe you cannot take credit.

[Gulfstream G450 Operational Information Supplement 02, page 19] For landing operations on a wet, grooved runway, data in this OIS will be conservative.

[Challenger 604 Operating Manual, §08-02-5, ¶1.B.] DRY RUNWAY: This category includes, in addition to those which are not "wet" or "contaminated", those paved runways which have been specially prepared with grooves or porous pavement and maintained to retain "effectively dry" braking action even when moisture is present.



Figure: Landing field lengths, from Pavement Grooving and Traction Studies, pages 109 and 110, figures 2 and 3.

We all know intuitively that a grooved runway makes it easier to stop. But braking on a wet, grooved runway as easy as on a dry runway? No, but it is more complicated than that:

  • Landing distances on a wet, grooved runway are remarkably reduced almost to the point of being dry, until the water depth is greater than 0.1 inch or if there is any slush. At that point the distances are improved but not nearly as much.
  • Balanced field lengths are "essentially dry" for grooved runways in a "wet and puddled" condition. If the runway is slush covered, the advantages of runway grooves are only "slight."

More about this: Grooved Runways.


Accident data bases appear to be devoid of mishaps caused by pilots assuming dry runway credit on grooved runways where they shouldn't.

Determining grooved runway effectiveness without gray areas

We think of the distance between dry runway and grooved runway performance as a gray area and for some aircraft it actually is. Tests show landing performance on a runway with as much as 0.1 inch of water is remarkably close to dry runway performance but from that point on the advantage decreases. Takeoff balanced field performance is improved, but not my as much. The regulations allow manufacturers to take credit for dry runways but few are willing to do so. There in lies the gray.

  • If your manuals say you can take credit for grooved runways and you follow their directions, you have no gray areas so long as you stay within the parameters provided.
  • If your manuals say you cannot take credit for grooved runways, you have no gray areas. You must operate assuming the grooved runway does not provided additional braking capability but realize you will reap some benefit in actual practice.
  • If your manuals are silent on the issue you have a gray area to deal with. You ask the manufacturer for a ruling, one way or the other, and assume no credit until they do.

Wind Shear —or— "It's little gusty"

A report of wind shear is sure to get our attention, except when it doesn't. The problem with wind shear is there are times when we know it can kill us and bears the utmost respect, and there are other times when we know it is just a jittery pilot report from someone who doesn't know the difference between a microburst and a gusty wind.

It is easy enough to put into writing: "In case of wind shear, go around." I've been in operations where this was the rule. But if you really did that, you would be going around routinely where other aircraft are landing uneventfully. It can be confusing. This does not, however, constitute a gray area. It is, rather, a lack of knowledge and precision in reporting. It can be combatted.

Regulations (14 CFR 91, 14 CFR 135, etc.)

[Advisory Circular 00-45G, ¶3.2 Pilot Weather Reports] Ten knots or more fluctuations in wind speed (+/- 10KTS), within 2,000 feet of the surface, require an Urgent (UUA) pilot report.

A pilot is well within his or her rights to report wind shear after losing 10 knots on final for no apparent reason. That pilot doesn't really know if it was wind shear and based on the report, neither do you.

[Advisory Circular 00-45G, ¶6.3.2 Graphical Airman's Meteorological Advisory] Low Level Wind Shear (LLWS) — LLWS is defined as wind shear below 2000 feet AGL, other than convectively induced, exceeding 10 knots per 100 feet (vector difference between two points in space).

[Advisory Circular 00-45G, ¶ Terminal Area Forecast]

  • Non-Convective Low-Level Wind Shear (LLWS) Group (WShwshwshws/dddffKT) Wind Shear (WS) is defined as a rapid change in horizontal wind speed and/or direction, with distance and/or a change in vertical wind speed and/or direction with height. A sufficient difference in wind speed, wind direction, or both, can severely impact airplanes, especially within 2,000 feet AGL because of limited vertical airspace for recovery.
  • Forecasts of LLWS in the TAF refer only to non-convective LLWS from the surface up to and including 2,000 feet AGL. LLWS is always assumed to be present in convective activity. LLWS is included in TAFs on an "as-needed" basis to focus the aircrew's attention on LLWS problems which currently exist or are expected.

Weather forecast reports can also cry wind shear with only 10 knots and quite often do so automatically if there is convective activity in the area.

[Aeronautical Information Manual, §7-1-26, ¶f.2.(a)] The LLWAS provides wind data and software processes to detect the presence of hazardous wind shear and microbursts in the vicinity of an airport. Wind sensors, mounted on poles sometimes as high as 150 feet, are (ideally) located 2,000 − 3,500 feet, but not more than 5,000 feet, from the centerline of the runway.

LLWAS will detect wind shear below 150 feet close to the airport and near the runway centerline. This can be helpful when dealing with a microburst or something that generates a windshear that starts high and extends to the surface, but it may be useless when dealing with a shear level caused by one air mass over another or something caused by obstacles higher than 150 feet.

[Aeronautical Information Manual, §7-1-26, ¶f.3.(a)] Terminal Doppler Weather Radar (TDWR). — TDWRs are being deployed at 45 locations across the U.S. Optimum locations for TDWRs are 8 to 12 miles off of the airport proper, and designed to look at the airspace around and over the airport to detect microbursts, gust fronts, wind shifts and precipitation intensities. TDWR products advise the controller of wind shear and microburst events impacting all runways and the areas 1/2 mile on either side of the extended centerline of the runways out to 3 miles on final approach and 2 miles out on departure.

TDWR is replacing LLWAS in many locations and seems to have a good track record. It will not, however, warn against wind shifts outside the arrival and departure ends of the runway. It can only detect wind shears associated with a microburst or gust front.

You may also hear the term "WSP," which stands for Weather System Processor. WSP is just like TDWR but it uses existing airport surveillance radar with upgraded technology.

These are lousy definitions of wind shear. Here is a better one . . .

[Approach and Landing Accident Reduction Tool Kit - windshear]

  • Windshear is a sudden change of wind velocity/direction.
  • The following types of windshear exist:
    • Vertical windshear (vertical variations of the horizontal wind component, resulting in turbulence and affecting aircraft airspeed when climbing or descending through the shear layer); and,
    • Horizontal windshear (horizontal variations of the wind component (e.g., decreasing head wind or increasing tail wind, or a shift from a head wind to a tail wind), affecting the aircraft in level flight, climb or descent).
  • windshear is associated usually with the following weather conditions:
    • Jet streams;
    • Mountain waves;
    • Frontal surfaces;
    • Thunderstorms and convective clouds; and,
    • Microbursts.
  • Microbursts present two distinct threats to aviation safety:
    • A downburst that results in strong downdrafts (reaching 40 knots vertical velocity); and,
    • An outburst that results in strong horizontal windshear and wind-component reversal (with horizontal winds reaching 100 knots).

Rules (Aircraft-specified)

Aircraft with the latest revisions of Enhanced Ground Proximity Warning Systems (EGPWS) or forward looking wind shear detection systems have a definite advantage but pilots should understand what these systems can and cannot do. For example . . .


Figure: G450 Windshear Alerting Envelope, from G450 Aircraft Operating Manual, §2A-34-50, figure 19.

[G450 Aircraft Operating Manual, §2A-34-50, ¶3.G.] Mode 7 - Detection Of Severe Windshear: (See Figure 19.)

  • Mode 7 is designed to provide alerts and warnings if the airplane encounters severe windshear. It is active between 10 and 1500 feet AGL and during takeoff, final approach and go-around.
  • Windshear caution alerts are annunciated if the windshear consists of an increasing headwind (or decreasing tailwind) and/or a severe updraft, which may precede an encounter with a microburst. In the event of a windshear caution, an amber WINDSHEAR icon is displayed on the PFD and an aural "WINDSHEAR, WINDSHEAR, WINDSHEAR" callout is annunciated. The alert remains active for as long as the airplane remains exposed to an increasing headwind and/or updraft condition in excess of the alert threshold.
  • Windshear warnings are annunciated if the windshear consists of a decreasing headwind (or increasing tailwind) and/or a severe downdraft. In the event of a windshear warning, a red WINDSHEAR icon is displayed on the PFD and an aural "WINDSHEAR, WINDSHEAR, WINDSHEAR" callout is annunciated. The aural callout will not repeat unless another separate severe windshear event is encountered. The WINDSHEAR icon remains displayed for as long as the airplane remains exposed to a decreasing headwind and/or downdraft condition in excess of the alert threshold. The alert threshold is adjusted as a function of available climb performance, flight path angle, airspeeds significantly different from normal approach speeds, and unusual fluctuations in static air temperature typically associated with the leading edge of microbursts.



Figure: Forces in the steady glide, from Connolly, Figure 11:8.

Even a 10-knot wind shear can be a big deal for aircraft with limited power, slow approach speeds, and unique handling characteristics. It can be a big deal for other aircraft as well since quite often you really don't know if a reported 10-knot wind shear is on its way to becoming a huge microburst in just a matter of minutes. But what about those days where there is no convective activity nearby, no evidence of an impending microburst, and it appears everyone is landing okay in gusty wind conditions? Why not just add some knots and accept a longer landing if the performance allows it?

Before you start adding knots to your approach speed, consider the following:

  • Brake energy — If you add a speed increment you should always assume you aren't going to bleed it off and that your brakes will have more work to do. If your brake energy limits prohibit the additive, you cannot assume the gust will die just as you touch down.
  • Deck angle (nose wheel strike) — Aircraft with exceptionally nose low approach angles could find themselves where the nose wheel is actually lower than the main gear just prior to the flare. If you fail to flare out the landing you could end up with a porpoised landing, at best, or substantial damage to the aircraft.
  • See Approach Speed Deck Angle

Many aircraft allow a 20 knot airspeed additive with the provision the speed be bled off prior to touchdown or, in some cases, prior to crossing the runway threshold. Reducing your approach speed by 20 knots between 100 and 50 feet may be the wrong thing to do, it sets the speed trend in the wrong direction just when you want it to be stable. Knowing how much extra speed your aircraft can and cannot accept for touchdown is something few manufacturers are willing to discuss and does constitute a gray area pilots must learn to deal with.

History (And more case studies)

The problem with microbursts is that they a short lived and conditions maybe okay for landing one minute and absolutely hazardous the next. If you suspect the conditions are ripe for microburst activity, you might want to find another airport.

See: Pan Am 759.

Flying into a cloud producing lightning is never a good idea, especially if you are moments away from landing.

See: Delta Airlines 191.

Once you've recognized you are in a real, no kidding, wind shear, you need to act decisively.

See: US Air 1016.

Determining wind shear with and without gray areas

You shouldn't be messing around with wind shear, no doubt about it. But if you went around every time you heard it on the radio, you wouldn't get anywhere. You need to understand what is a reliable windshear report and what isn't.

If you see a TAF or METAR report of wind shear, you might be dealing with an automated response to convective activity. If you hear a pilot report, especially from a light aircraft, you might be dealing with gusty winds. In all these cases, further investigation is needed and if your aircraft performance permits, you might be able to continue.

Automated reports from LLWAS, TDWR, WSP, or airborne EGPWS equipment must be taken seriously. Listen to pilot reports as they are given to tower, you can learn a lot from a pilot's tone of voice. I've heard of a pilot report that ended with, "tower, if you let anyone land in this you insane."

More about this: Wind Shear.

135 En Route, Start / End 91 Duty Limits —or— "No pax / no worries"

The question here is when you start a day under 14 CFR 91 and pick up a 14 CFR 135 trip, when did your duty period begin? Conversely, if you start a 14 CFR 135 trip, how are your duty limits impacted after you drop the passengers and continue your day without them? If you read 14 CFR 135 carefully you can come up with an answer that satisfies your desires (either way), but you must make sure that is okay with your POI before doing anything beyond the strictest interpretation.

Regulations (14 CFR 91, 14 CFR 135, etc.)

[14 CFR 135, §135.261] Applicability.

Sections 135.263 through 135.273 of this part prescribe flight time limitations, duty period limitations, and rest requirements for operations conducted under this part as follows:

(a) Section 135.263 applies to all operations under this subpart.

(b) Section 135.265 applies to:

(1) Scheduled passenger-carrying operations except those conducted solely within the state of Alaska. "Scheduled passenger-carrying operations" means passenger-carrying operations that are conducted in accordance with a published schedule which covers at least five round trips per week on at least one route between two or more points, includes dates or times (or both), and is openly advertised or otherwise made readily available to the general public, and

(2) Any other operation under this part, if the operator elects to comply with §135.265 and obtains an appropriate operations specification amendment.

(c) Sections 135.267 and 135.269 apply to any operation that is not a scheduled passenger-carrying operation and to any operation conducted solely within the State of Alaska, unless the operator elects to comply with §135.265 as authorized under paragraph (b)(2) of this section.

14 CFR 135, §135.263 Flight time limitations and rest requirements: All certificate holders.

14 CFR 135.261, above, says this section applies to operations under this subpart. That refers to "Subpart F - Crewmember Flight Time and Duty Period Limitations and Rest Requirements."

(a) A certificate holder may assign a flight crewmember and a flight crewmember may accept an assignment for flight time only when the applicable requirements of §§135.263 through 135.271 are met.

(b) No certificate holder may assign any flight crewmember to any duty with the certificate holder during any required rest period.

(c) Time spent in transportation, not local in character, that a certificate holder requires of a flight crewmember and provides to transport the crewmember to an airport at which he is to serve on a flight as a crewmember, or from an airport at which he was relieved from duty to return to his home station, is not considered part of a rest period.

(d) A flight crewmember is not considered to be assigned flight time in excess of flight time limitations if the flights to which he is assigned normally terminate within the limitations, but due to circumstances beyond the control of the certificate holder or flight crewmember (such as adverse weather conditions), are not at the time of departure expected to reach their destination within the planned flight time.

[14 CFR 135, §135.265] Flight time limitations and rest requirements: Scheduled operations.

(a) No certificate holder may schedule any flight crewmember, and no flight crewmember may accept an assignment, for flight time in scheduled operations or in other commercial flying if that crewmember's total flight time in all commercial flying will exceed—

(1) 1,200 hours in any calendar year.

(2) 120 hours in any calendar month.

(3) 34 hours in any 7 consecutive days.

(4) 8 hours during any 24 consecutive hours for a flight crew consisting of one pilot.

(5) 8 hours between required rest periods for a flight crew consisting of two pilots qualified under this part for the operation being conducted.

A scheduled operation is defined earlier as in accordance with a published schedule which covers at least five round trips per week and is openly advertised. The limits appear to apply to these operations and all commercial flying. Can you fly several hours of non-commercial flying and then start 8 hours of commercial flying? It is not clear in the regulation.

(b) Except as provided in paragraph (c) of this section, no certificate holder may schedule a flight crewmember, and no flight crewmember may accept an assignment, for flight time during the 24 consecutive hours preceding the scheduled completion of any flight segment without a scheduled rest period during that 24 hours of at least the following:

(1) 9 consecutive hours of rest for less than 8 hours of scheduled flight time.

(2) 10 consecutive hours of rest for 8 or more but less than 9 hours of scheduled flight time.

(3) 11 consecutive hours of rest for 9 or more hours of scheduled flight time.

A "rest period" is defined as "the period free of all responsibility for work or duty should the occasion arise." This makes this section a little more clear cut, any flight duties on behalf of the operator should count.

(c) A certificate holder may schedule a flight crewmember for less than the rest required in paragraph (b) of this section or may reduce a scheduled rest under the following conditions:

(1) A rest required under paragraph (b)(1) of this section may be scheduled for or reduced to a minimum of 8 hours if the flight crewmember is given a rest period of at least 10 hours that must begin no later than 24 hours after the commencement of the reduced rest period.

(2) A rest required under paragraph (b)(2) of this section may be scheduled for or reduced to a minimum of 8 hours if the flight crewmember is given a rest period of at least 11 hours that must begin no later than 24 hours after the commencement of the reduced rest period.

(3) A rest required under paragraph (b)(3) of this section may be scheduled for or reduced to a minimum of 9 hours if the flight crewmember is given a rest period of at least 12 hours that must begin no later than 24 hours after the commencement of the reduced rest period.

(d) Each certificate holder shall relieve each flight crewmember engaged in scheduled air transportation from all further duty for at least 24 consecutive hours during any 7 consecutive days.

14 CFR 135, §135.267] Flight time limitations and rest requirements: Unscheduled one- and two- pilot crews.

(a) No certificate holder may assign any flight crewmember, and no flight crewmember may accept an assignment, for flight time as a member of a one- or two-pilot crew if that crewmember's total flight time in all commercial flying will exceed—

(1) 500 hours in any calendar quarter.

(2) 800 hours in any two consecutive calendar quarters. (3) 1,400 hours in any calendar year.

(b) Except as provided in paragraph (c) of this section, during any 24 consecutive hours the total flight time of the assigned flight when added to any other commercial flying by that flight crewmember may not exceed—

(1) 8 hours for a flight crew consisting of one pilot; or

(2) 10 hours for a flight crew consisting of two pilots qualified under this part for the operation being conducted.

Here is where it gets messy. When is a flight "assigned?" If you are scheduled to fly your passengers in 9 hours with a drop off at White Plains and then another hour empty to your home base, no problem. But let's say the winds are against you and it takes ten hours and a few minutes to get to White Plains. Under 14 CFR 135.261(d) there is no problem as the winds can be considered circumstances beyond your control. But now can you continue the trip home under 14 CFR 91? Wasn't that flight assigned?

(c) A flight crewmember's flight time may exceed the flight time limits of paragraph (b) of this section if the assigned flight time occurs during a regularly assigned duty period of no more than 14 hours and—

(1) If this duty period is immediately preceded by and followed by a required rest period of at least 10 consecutive hours of rest;

(2) If flight time is assigned during this period, that total flight time when added to any other commercial flying by the flight crewmember may not exceed—

(i) 8 hours for a flight crew consisting of one pilot; or

(ii) 10 hours for a flight crew consisting of two pilots; and

(3) If the combined duty and rest periods equal 24 hours.

(d) Each assignment under paragraph (b) of this section must provide for at least 10 consecutive hours of rest during the 24-hour period that precedes the planned completion time of the assignment.

(e) When a flight crewmember has exceeded the daily flight time limitations in this section, because of circumstances beyond the control of the certificate holder or flight crewmember (such as adverse weather conditions), that flight crewmember must have a rest period before being assigned or accepting an assignment for flight time of at least—

(1) 11 consecutive hours of rest if the flight time limitation is exceeded by not more than 30 minutes;

(2) 12 consecutive hours of rest if the flight time limitation is exceeded by more than 30 minutes, but not more than 60 minutes; and

(3) 16 consecutive hours of rest if the flight time limitation is exceeded by more than 60 minutes.

(f) The certificate holder must provide each flight crewmember at least 13 rest periods of at least 24 consecutive hours each in each calendar quarter.

There are further stipulations for unscheduled three- and four-pilot crews in 14 CFR 135.269, for helicopter hospital emergency medical evacuation services in 14 CFR 135.271, and for flight attendants under 14 CFR 135.273.

Where you fall on this issue might depending on what you want to do: get paid for another day on the road or get home. Or you just might have an interpretation you firmly believe that others disagree with, just as firmly.

Rules (Company-specified)

Some operators remove all doubt by making a conservative ruling. One of the 14 CFR 135 operators in my past clearly stated: "Duty Time is defined as commencing at the scheduled no-go time or one hour prior to scheduled departure, whichever is greater, and ending one-half hour following the actual time of arrival." Regardless of how you interpret the regulation, your operator has constrained you and you must follow their rules.

If your operator does not rule one way or another, you should ask. Otherwise . . .


There are operators who come down on either side of each of the issues:

  • You can start your day under 14 CFR 91 and the clock for 14 CFR 135 doesn't start until the first 135 leg. . . . OR . . . Any 135 duty period must include all activity after the rest period ended.
  • You can finish your 14 CFR 135 day and start a 14 CFR 91 day as a separate entity. . . . OR . . . If the end of the day was part of your schedule, it must be considered a part of 135 duty period.

I doubt any of these operators are acting on their own, I am betting each has a phone call from their POI supporting their position. But how can they be different? As a 14 CFR 135 check airman I once vented to our Principal Operations Inspector about the futility of getting straight answers from one flight standards region that can be reliably backed up in other regions. It sometimes seems the answer you get depends on where in the country you are. He explained the problem succinctly: "The FAA is comprised of 82 flight standards district offices, each independently owned and operated."

Determining Duty Limits without gray areas

I used to think the best way to handle this situation is to pick up the phone and call your POI. If the POI rules one way or the other, you have your answer. If the POI waffles, then you probably ought to go the conservative route: it is all 135 time, before and after.

Watching the FAA throw the rules out during their vendetta against TAG Aviation taught me you cannot trust them to be consistent or to honor commitments made by individual POIs. You may get a POI to tell you that last leg is not considered a part of your commercial day so go ahead and consider it 14 CFR 91. But you need to realize there is more at risk than you and your airplane. Let's say you land at the end of the day but have a minor problem that causes you to delay on the runway. It is late at night and the tower clears the commercial airliner behind you to land, right on top of you, killing everyone on board both aircraft. The FAA is going to be looking for a scape goat and it could very well be you and your operator. Yes I am paranoid. You don't have to be, but I would recommend it.

Departure Obstacle Avoidance

I often get asked "How can I be sure I'm going to clear an obstacle if I lose an engine after I've retracted my flaps and have accelerated above V2 to V2+10 when the charts are based on losing an engine at V1, climbing out with the flaps set at those speeds? It gets worse. What if you do all that and lose an engine after your flaps are up?

Figure: Obstacle clearance, three scenarios, from Eddie's notes.

In the drawing there are four scenarios, two of which guarantee obstacle clearance and two which leave you with question marks:

  1. Green solid line — If you load your airplane up to assure obstacle clearance One Engine Inoperative (OEI) or All Engines Operating (AEO) using the appropriate planning, climb with your flaps set as planned, and fly at the recommended speed (i.e., V2 to V2+10), you will be okay if you fly with the required precision even if you lose an engine at any point from V1 all the way through obstacle clearance.
  2. Blue line — If you load your airplane up to assure obstacle clearance One Engine Inoperative (OEI), climb with your flaps set as planned, and fly at the recommended speed (i.e., V2 to V2+10), you will be okay if you fly with the required precision.
  3. Green dashed line — If you took the steps to assure obstacle clearance under scenarios 1 or 2 above, but after you takeoff decide you are going to accelerate above the target speed and clean up the airplane, you don't know if you are going to clear the obstacle, even if you don't lose an engine.
  4. Red line — If you took all the steps to assure obstacle clearance under scenarios 1 or 2 above, but after you takeoff decide you are going to accelerate above the target speed and clean up the airplane, and then you lose an engine, you are even more trouble. The best you can do is pull the nose up to catch the appropriate engine-out, flaps up speed (i.e., VSE). Even if you do this, you don't know if you are going to clear the obstacle.

This isn't so much a gray area as a pilot error in understanding what it takes to clear an obstacle. The only way to assure obstacle clearance is to fly the target speed in the correct configuration until the obstacles are cleared. Does that mean you need to subject your passengers to a rocket ship ride even if you don't lose an engine on the runway? Not necesarily. If you understand where the obstacles are you can adjust your clean up altitude appropriately.

In our Departure Obstacle Avoidance / Aspen Example, we know the required climb gradient is dictated by two obstacles at 4.5 and 7.2 nm north of the airport, the higher of which is 9,250' MSL (1,570' above the departure end of the runway). We should plan on maintaining V2 to V2+10 until we've climbed above this altitude, even if we don't lose an engine. Now we know we can beat the obstacle following an engine failure at V1, at our planned level off altitude, or anywhere in between.


14 CFR 1, Title 14: Aeronautics and Space, Definitions and Abbreviations, Federal Aviation Administration, Department of Transportation

14 CFR 25, Title 14: Aeronautics and Space, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation

14 CFR 91, Title 14: Aeronautics and Space, General Operating and Flight Rules, Federal Aviation Administration, Department of Transportation

14 CFR 135, Title 14: Aeronautics and Space, Operating Requirements: Commuter and On Demand Operations and Rules Governing Persons on Board Such Aircraft, Federal Aviation Administration, Department of Transportation

Advisory Circular 00-45G, Aviation Weather Services, July 29, 2010, U.S. Department of Transportation

Advisory Circular 20-117, Hazards Following Ground De-Icing, March 29, 1988, U.S. Department of Transportation

Aeronautical Information Manual

Challenger 604 Operating Manual, Publication No. CH 604 OM, Rev 56, Jan 14/05.

Connolly, Thomas F., Dommasch, Daniel 0., and Sheryby, Sydney S., Airplane Aerodynamics, Pitman Publishing Corporation, New York, NY, 1951.

Flight Safety Foundation, Approach and Landing Accident Reduction Tool Kit - windshear, August-November 2000

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Operational Information Supplement, G450-OIS-02, Contaminated Runway Performance, Revision 1, August 3, 2011

FAA Pilot/Controller Glossary, PCG, 8/22/13

ICAO Doc 9640 - Manual of Aircraft Ground De-icing/Anti-icing Operations, International Civil Aviation Organization, 2000

Revision: 20160501