The Great Escape
Diverting from an oceanic track to an alternate requires a plan
I've had a few jobs where one of my primary duties was to teach others how to fly internationally. I liked to end the training with this:
The art of international operations includes the science of knowing how to pickup the pieces when they fall.
And they will fall!
- The Real World — Of course the real world has several different regions and some oceanic tracks are more crowded than others. So let's look at the North Atlantic as a worst case scenario.
- Aircraft Theory — The manufacturer has made assumptions about what you are going to do when they promise a certain level of performance. The people who did your ETP math are using those assumptions.
- Regulatory Theory — ICAO Doc 4444 and a few others have a lot to say on what you are expected to do when leaving an oceanic track.
- Reality — Every situation is different and it will be up to you to find a good compromise.
- Waypoint Briefing — Your situation changes as the flight progresses and the best way to have the most current "Plan B" in mind is to update any contingency briefings just prior to each waypoint.
- Improving Your Odds Before You Leave the Ground — Most ETP computations depend on the crew filing optimal altitudes; and landing with minimum fuel. Can you change those assumptions?
- 180 Degree Turn at Altitude — If you want to turn around, you may be encroaching on more airspace than you think. What is your turn diameter at altitude?
- Polar Alternates — An alternate airport might be the right choice if you have a fuel leak and are about to become a glider or you have a fire and you are about to become charcoal. But that same airport might not be a wise choice for a medical emergency or a depressurization that leaves you other options.
First of all, hardly anything ever goes wrong. You can go an entire career without ever having to divert from an oceanic track. (In almost 40 years of doing this, I can count the number of times I've had to do this on one hand.)
Well the good people who built your airplane have a definite idea about what to do when an engine quits. The people who computed your flight plan have a solid idea of how to best compute an Equal Time Point (ETP) and what it will take to get the airplane safely on the ground with the available fuel.
The people who designed that airspace and those tracks don't really care about your aircraft theory because they have a theory of their own.
But you don't want to do that. If you keep your wits about you and communicate your intentions, perhaps you can work and play well with others even when diverting off an oceanic track.
Improving your odds, one waypoint at a time . . .
Improving your odds with better planning . . .
Sometimes you just want to go home, turn around and retreat. It isn't as straight forward as you might think.
Finally, just because you have an alternate doesn't mean going there is a wise decision. This holds true especially at high latitudes.
The Real World
In most parts of the world, an oceanic track is designed to keep you separated from aircraft on adjacent tracks. You cannot turn off the track without considering the possibility of a midair collision first. With or without adjacent tracks, no matter where in the world you are, you need to have an idea where the nearest suitable alternate is at all times.
Photo: A random route above the North Atlantic Track System, from Eddie's notes.
Click photo for a larger image
Let's say you are flying to Europe either on or above the northernmost North Atlantic Track when an engine quits just as you pass 56°North 030° West. You need to descend and your best option is to head to Shannon, Ireland (EINN).
The aircraft manufacturer should have evaluated your aircraft's performance and figured out the best way to squeeze the most distance for the least amount of gas in the event of an engine failure. They will have made similar computations for a depressurization scenario and for a simple diversion while remaining at altitude.
At the very least you should have made computations to figure at what point along your route of flight you can make the decision to continue or return to a set of alternate airports in front or behind you. This point is the Equal Time Point (ETP) and is a staple of international operations. Your flight planning service very likely makes these computations for you. But what are the assumptions behind the numbers?
AFM Drift Down Procedure
Your ETP is probably designed for you to do the following:
- Set your operating engine(s) to a maximum thrust setting, while turning directly to your alternate
- Allow your speed to decay to drift down speed while maintaining altitude (this may happen almost immediately or in a minute or so for most two-engine aircraft)
- As drift down speed is reached, descend at that speed until at drift down altitude
This gets you to your ETP alternate at the predicted fuel level, provided the winds, temperature, and other considerations cooperate. In other words, it is a best case scenario. But what is the route of flight for this diversion?
Many pilots assume that when they approach an Equal Time Point (ETP), they will have smooth sailing getting to either ETP airport. It is a safety factor, after all. But they may be surprised to hear that most ETP calculations assume a straight line route of flight and do not provide for approach fuel or any additional fuel needed for the approach or APU.
For more about ETP calculations, see: Equal Time Points.
Yup, the ETP is based on a straight line. In a G450 at common weights, for example, the cruise speed of 0.80 Mach is identical to your drift down speed, it will take you 38 minutes and 254 nautical miles to descend to your drift down altitude of 29,000 feet. Unfortunately this means crossing two tracks to your south.
Photo: Turning direct to the alternate, descending through an adjacent track, from Eddie's notes.
Click photo for a larger image
In our example, that would mean a twin-engine turned single-engine Gulfstream would turn right off Track "A" and would end up crossing Track "B" about 100 nm west of 020° west. The descent is begun immediately, possibly encroaching on lower traffic on Track "A" and probably also those on Track "B" using the expected descent rate. Because the center tracks are now spaced at half a degree latitude, our descent may actually cross a third track before reach an altitude below the tracks. The crew can expect to make it to Shannon with the amount of fuel promised by their ETP calculations, provided they avoid hitting anyone.
Photo: Fuel remaining in a CL601 flying from California to Hawaii, from a friend of Eddie's.
Click photo for a larger image
You may argue that it just doesn't matter, since you normally carry enough gas for every situation. That is true for some situations but not all. In the example above, a Challenger 601 can make Santa Ana, California to Kona, Hawaii without too much trouble. But if they were to lose cabin pressurization at their KSFO - PHOG Equal Time Point, they could find themselves on final with just enough gas for one approach.
What about an "ultra long range" aircraft like a GV? I once flew a GV from Wilmington, Delaware to Kona, Hawaii and landed with enough gas to make California without refueling. But a GV from Paris to Los Angeles can find itself with similarly paltry amounts of fuel flying over desolate regions of Canada. The critical lesson here is that you cannot assume you are going to be okay at an ETP alternate just because you will have lots of gas when you land at your planned destination.
There are two basic procedures now. For everywhere in the world except the North Atlantic, you should remember 45 degrees at 15 nautical miles offset. Some people call this the "Quad Four Maneuver" since it came from ICAO Doc 4444; it is as good a name as any, I suppose.
Regardless of what you call it, you should have it memorized:
- Turn 45° away from track,
- Pick a direction based on alternates, nearby tracks, SLOP, and desired altitude,
- Obtain a 15 NM offset,
- Pick an altitude 500 ft off if at or below FL 410, 1000 ft if above,
- Broadcast to ATC and nearby aircraft
- Light up the airplane.
For the North Atlantic, as of 28 March 2019, things are a bit more complicated. You are now looking at 30 degrees and 5 nautical miles offset. (See the diagram, kindly provided by https://ops.group/.)
General ICAO Guidance
[ICAO Doc 4444, ¶18.104.22.168] If an aircraft is unable to continue the flight in accordance with its ATC clearance, and/or an aircraft is unable to maintain the navigation performance accuracy specified for the airspace, a revised clearance shall be obtained, whenever possible, prior to initiating any action.
[ICAO Doc 4444, ¶22.214.171.124] The radiotelephony distress signal (MAYDAY) or urgency signal (PAN PAN) preferably spoken three times shall be used as appropriate. Subsequent ATC action with respect to that aircraft shall be based on the intentions of the pilot and the overall air traffic situation.
[ICAO Doc 4444, ¶126.96.36.199] If prior clearance cannot be obtained, until a revised clearance is received the following contingency procedures should be employed and the pilot shall advise air traffic control as soon as practicable, reminding them of the type of aircraft involved and the nature of the problem. In general terms, the aircraft should be flown at a flight level and on an offset track where other aircraft are least likely to be encountered. Specifically, the pilot shall:
- leave the assigned route or track by initially turning at least 45 degrees to the right or to the left, in order to acquire a same or opposite direction track offset 15 NM (28 km) from the assigned track centreline. When possible, the direction of the turn should be determined by the position of the aircraft relative to any organized route or track system. Other factors which may affect the direction of the turn are:
- the direction to an alternate airport;
- terrain clearance;
- any strategic lateral offset being flown; and
- the flight levels allocated on adjacent routes or tracks;
- having initiated the turn:
- if unable to maintain the assigned flight level, initially minimize the rate of descent to the extent that is operationally feasible (pilots should take into account the possibility that aircraft below on the same track may be flying a 1 or 2 NM strategic lateral offset procedure (SLOP)) and select a final altitude which differs from those normally used by 150 m (500 ft) if at or below FL 410, or by 300 m (1,000 ft) if above FL 410; or
- if able to maintain the assigned flight level, once the aircraft has deviated 19 km (10 NM) from the assigned track centreline, climb or descend to select a flight level which differs from those normally used by by 150 m (500 ft) if at or below FL 410, or by 300 m (1,000 ft) if above FL 410;
- establish communications with and alert nearby aircraft by broadcasting, at suitable intervals on 121.5 MHz (or, as a backup, on the inter-pilot air-to-air frequency 123.45 MHz) and where appropriate on the frequency in use: aircraft identification, flight level, position (including the ATS route designator or the track code, as appropriate) and intentions;
- maintain a watch for conflicting traffic both visually and by reference to ACAS (if equipped);
- turn on all aircraft exterior lights (commensurate with appropriate operating limitations); and
- keep the SSR transponder on at all times.
For more about the "Quad Four Maneuver" see: Oceanic Contingencies.
Each region of the world may have specific procedures that are expected of you during a contingency that you may or may not want to follow. Your ETP fuel allowances, for example, may not permit following the region's expectations. But you should know what is expected of you so you can best decide how to proceed. In the North Atlantic, for example:
[ICAO Doc 7030, §NAT, ¶188.8.131.52] Descent through the MNPS airspace
- An aircraft that is not MNPS/RVSM-approved and is unable to maintain a flight level above MNPS/RVSM airspace should descend to a flight level below MNPS/RVSM airspace.
- An aircraft compelled to make a descent through MNPS airspace, whether continuing to destination or turning back, should, if its descent will conflict with an organized track:
- plan to descend to a level below FL 280;
- prior to passing FL 410, proceed to a point midway between a convenient pair of organized tracks prior to entering that track system from above;
- while descending between FL 410 and FL 280, maintain a track that is midway between and parallel with the organized tracks; and
- contact ATC as soon as practicable and request a revised ATC clearance.
Flying the ICAO Doc 4444 maneuver prevents us from crossing or descending through tracks, but will cost us in terms of time and fuel.
- Turn 45° away from track while maintaining altitude
- Allow your speed to decay while in level flight (probably below optimal drift down speed) until we have established a 15 nm offset
- Turn 45° to parallel the tracks
- Descend below the tracks (FL 280 in the North Atlantic)
- Turn direct once below the tracks
Photo: Flying the Quad Four Procedure, flying between adjacent tracks, from Eddie's notes.
Click photo for a larger image
The Quad Four maneuver will cost us fuel because we end up below drift down speed until our offset is established and because we fly additional distance in the turns away and parallel the tracks. In the case of our Gulfstream, we will also use extra fuel because an altitude below FL280 will probably be below our optimal drift down altitude.
It would seem to be a conundrum:
- a straight line to your alternate while minimizing altitude loss (as aircraft theory would demand) gets you to your alternate airport with the predicted fuel but risks a midair collision, but
- flying ICAO descents, altitudes, and routes (as regulatory theory would have you do) avoids the midair but risks a water landing.
What's a pilot to do?
Every situation is different but you need to come up with a way to minimize risk while maximizing survivability. Here is a possible solution for our example scenario. It is up to you to come up with an escape plan for each of your oceanic route segments.
Photo: Flying the "Safe Zone" Procedure, flying between adjacent tracks, from Eddie's notes.
Click photo for a larger image
While each situation is different, looking at the big picture you can come up with a plan to maximize the use of "safe zones" between tracks. In our example:
- We enter a direct leg to the next waypoint, one leg to the south (5520N).
- We maintain altitude (and sacrifice drift down speed) while making note of the ETE to the next waypoint.
- At one-fourth of the ETE we know we are one-fourth of the total distance between tracks (60 nm in this example) and therefore beyond 15 nm and safe to begin our descent.
- We realize that we must be below the tracks by three-quarters of our ETE so we use our FMS vertical navigation to plan a descent that has us level when 15 nm of the next track.
This method isn't as efficient as the AFM procedure but offers greater assurance of not encroaching on another aircraft's airspace. This method will, however, get us to the alternate with more gas than the purely Quad Four maneuver. Each situation is different, this should provide an example of the type of "heads up" thinking that will serve you well.
Depending on your aircraft, the time between an engine failure and needing to start down can be only seconds. Many twin-engine aircraft cruise right at their drift down speeds (such as a Gulfstream G450). Others give you more time (like a Challenger 605). Aircraft with three or more engines can give you 20 or 30 minutes (such as a Falcon 900). But no matter the amount of time you have, you should know what to do before it happens. A good time to think about this is at each waypoint. As your geography (distance along the route), performance (reduce weight), and endurance (reduced fuel) change, your situation changes. You need to brief a new escape plan at every waypoint.
At each waypoint you should:
- Brief the aircraft's current weight
- Look up and brief the current drift down speed and altitude
- Update the weather at any applicable alternates
- Brief the proximity of any organized tracks relative to the next leg
- Brief the planned direction of turn as well as the route and altitude needed to avoid any organized tracks (your escape plan)
Improving Your Odds Before You Leave the Ground
At the very least, you can look at your ETP fuel remaining calculation and decide to takeoff with more fuel, then replan at the higher weight and possibly lower altitudes. If your flight planning service allows some customization, you might be able to dial in these extra margins automatically.
- The distance is a direct line from the ETP to the alternate airport; it doesn't make any allowance for having to circumnavigate any tracks, vectors around traffic, or to make an instrument approach.
- In a depressurization scenario, you end up at 10,000 or 12,500 feet. Will the cabin be warm enough? Maybe 10,000 feet is too high? How much fuel will it take to fly lower?
- In a drift down scenario, the pure math assumes you will be descending according to the manufacturer's drift down procedures. But will you be able to do that if there are any tracks between you and the alternate?
Photo: ARINC Direct ETP Presets
Your flight planning service may allow you to add factors to your ETP fuel computations. ARINC Direct, for example, adds a default 45 minutes of holding at the ETP airport at 1,500 feet AGL at AFM holding speeds. You can change many of the calculation assumptions directly on the "Create Flight Plan" page. Here are a few ideas on how to best customize this:
- 1E INOP Calculation — If your aircraft has a drift down altitude above FL280 for most weights, lowering the value to FL275 will add enough fuel to make sure you have enough fuel to fly below the tracks.
- Depressurized Calculation — Some aircraft have more oxygen than fuel, with others it is the opposite. No matter your situation, you should realize the passenger masks on most aircraft are only good enough to get them from altitude to unpressurized altitudes.
180 Degree Turn at Altitude
Making a 180° turn at altitude isn't as simple as one might think. At most crossing altitudes your true airspeed will be very high, 400 knots or higher. Your available bank angle will be less, say around 17° or so. If you are on track with 30 nautical mile spacing, you will be getting very close to your neighbors. It is something to consider.
Computing your turn radius is simply a matter of dividing your true airspeed by the mathematical tangent of your bank angle and a magical factor:
r = turn radius, ft
V = velocity, knots (TAS)
θ = bank angle, degrees
More about this: Turn Performance.
Of course the turn diameter is double this and you also need to figure on wind effects.
In the case of a Gulfstream 450 and FL410 doing 0.80 Mach (around 460 KTAS), limited to 17° of bank, the turn radius is just a bit over 10 nm which means the diameter is just over 20 nm. If you are on a Reduced Lateral Separation track, with only 30 nm between tracks, the distance gets eaten up quickly. If you are flying east bound with a 2 nm Strategic Lateral Offset Procedure (SLOP) and need to turn right, you could end up 30 - 2 - 20 = 8 nm of the next track.
Imagine a scenario where you are flying above 70° North latitude and still have five hours left in the flight. One of your passengers appears to be suffering a stroke. You have an alternate right in front of you. Easy decision, right? Not so fast.
More about this: High Latitude Operations.
Figure: Arctic Alternates, (Eddie's notes)
The problem with some remote alternates:
- No (or very limited) medical facilities — That MedAire kit on your airplane might just be better that what you find within hours of your alternate airport. You might be better off dialing that MedAire phone number and seeing if your passenger would be better off with some of the drugs in that kit while just a few hours away from a city with a real hospital.
- No (or very limited) fuel — Sometimes you don't have an option, but you might be putting your airplane down someplace where it will have to remain for a few months.
- Very limited transportation options — If your passengers need to get out, or your mechanic needs to get in, the alternate airport may be fairly inaccessible.
- No (or very limited) lodging options — It's going to be cold and you are going to have passengers and crew that may be placed in medical jeopardy having to sleep in an unheated hangar (if they are lucky) or worse.
Commercial Operations Notes
Things get a little more complicated for commercial operators, but usually for the better. Part 121 operators, for example, need to consider many (but not all) of the problems I've shown here. A helpful reader brings any of these up and has graciously agreed to share them with you.
Even those of us who fly purely under Part 91 can take a few of these points as best practices.
Have read your articles forever. I appreciate the depth of thought that goes into them in trying to make the pilots safer people who THINK and aren’t just fancy FMS-typists.
A couple of other issues that are required under 121.646 that it would behoove our 91/135 brethren to consider:
- APU use. If you lose an engine, 121 Boeing people have to light the APU and account for that fuel burn (180#/hr NG and 500#/hr Classic)
- Icing. There are several ways to account for it legally. You have to account for both the amount of additional gas spent to anti-/de-ice the aircraft and DRAG caused by ice accretion on non-protected parts of the airplane for 10% of the time you are in icing. That is A WHOPPING 29% increase for the 737-500.
- A missed approach – after all this, you think you will perform well at minimums skippy? Wouldn’t it be nice to have some extra in case you had to come at it again once your heart rate was below 190 bpm? ETOPS rules required this up to 2009, then they dropped it from 121 requirements, but we still have it in our flight plans.
- Alternate weather. Most 135 operators have C055 which requires pads to the operational minimums at release. But 121 carriers have to have those pads as well as a suitable window from the EARLIEST time you could use the alternate to the LATEST time you could use it (that could be 5+ hours for your outbound). The confidence in having that alternate is far greater if it has to meet these requirements at flight release. They drop to operational mins at ETA once more than 60 min from an adequate airport (SE) but having the pads is a conservative measure.
- Wind errors: require an additional 5% fuel for wind error forecasting. While the global models from most providers are spot on, I have had several days where it looks like the computer was on break during the forecasting phase.
- Mandatory “two heads” flight planning scrutiny. With scheduled carriers, a dispatcher and PIC BOTH have to sign the flight release to make sure the other didn’t muck it up. We have flight followers who are dispatchers in all but name and it REQUIRES that both read the flight plans and agree before they sign it. One of the easiest ways to screw up: planning something for NOW using winds for TOMORROW. (checking the flight plan “calculated” time is BEFORE the ETD is a mandatory part of our checklist). That’s just one example where two heads can prevent disaster from a planning standpoint.
- 5% additional fuel unless you are part of a fuel monitoring program. If your aircraft model is tweaked to be N-number specific, awesome. But if it’s a fleet model and your aircraft has more than a few cycles on it, probably not going to get that “new airplane” efficiency. Consequently, they MANDATE additional fuel unless your model is your own.
Just some thought to consider.
ICAO Doc 4444 - Air Traffic Management, 16th Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, October 2016
ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2008
ICAO Doc 7030, Amendment 1, International Civil Aviation Organization, 8 January 2009
ICAO Doc 7030, Amendment 9, International Civil Aviation Organization, 2 October 2017