Eddie Sez:

Takeoff data in the G450 is usually easy unless it is difficult. So let's make it easy when we can:

  • Basis for data — The assumptions behind almost all of the data comes from the AFM, you need to have these in mind for all that follows.
  • Performance Computer — The FMS can handle almost all of your takeoff data needs, including rated or flex data, 10° or 20° flaps, dry or wet surface conditions, and a variety of anti-ice combinations. It will even compute a flex takeoff on a wet runway and you can input a number of obstacles or a SID gradient requirement. It cannot handle contaminated runways, however.
  • Performance Handbook — The PH gives you contaminated runway data for three depths of water, slush, and snow, that you will not find in the Performance Computer. While you can interpolate between the depths, these numbers tend to be conservative.
  • Aircraft Flight Manual — The AFM provides a way to compute reduced data on a wet runway, either graphically (Section 5) or with tabular data (Appendix A). Section 5 allows reduced takeoffs with tailwinds and on a wet runway. The AFM does not, however, consider contaminated runways.
  • Operational Information Supplement OIS-02 — OIS-02 provides contaminated takeoff and landing distance data.

Those are a lot options, but if you agree you won't be going reduced with a tailwind or downhill slope; and want to avoid graphical charts at all costs, you can go with the following game plan to cover every situation:

  1. Dry or Wet runway (Rated or Flex), 10° or 20° flaps: Use the FMS performance computer.
  2. Manual Data: Use AFM Appendix A.
  3. Obstacles: If they are simple you can still use the FMS performance computer. Otherwise, consider Departure Obstacle Avoidance software.
  4. Contaminated Runway (Certain Conditions): Use OIS-02, Section C.
  5. Contaminated Runway (Other Conditions): Use OIS-02, Section B.

Should you survive all that, I've added three other issues you might consider: Flex versus Rated, Flaps 20° versus 10°, and Anti-ice On versus Off.

Everything here is from the references shown below, with a few comments in blue.


Basis For Data

[G450 Airplane Flight Manual §5.1]:

  1. Approved engine thrust ratings are based on a minimum engine including allowances for installation, air bleed, and accessory items. The right engine is considered to be the critical engine for engine failure.

  2. Takeoff thrust is available for a maximum time of 10 minutes for emergency, engine-out operations and is used through the takeoff and second segment climb. The Takeoff Thrust setting is also used for the evaluation of approach climb capability.

  3. Go-around thrust is used for computing the all-engines operating landing climb capability.

  4. Maximum continuous thrust is used for computing en route climb capabilities.

  5. Full temperature accountability within the operational limits, except for landing distance which is based on standard day.

  6. Hard-surfaced runway. Both dry and wet runway performance is included.

  7. Wind corrections are calculated with the following conservatism factors : 50% headwind or 150% tailwind. All charts should be entered with tower reported winds.

  8. Corrections for the use of anti-ice and, where applicable, ice accumulation on unheated surfaces are provided.

  9. Drag index corrections are intended for special mission aircraft with a higher drag level than the basic G450 commercial aircraft. Drag index values are presented from 0 to 50 on all charts adversely impacted by additional drag. The Drag index for the basic G450 aircraft is “0”, and therefore, there is no need to apply any drag index corrections.

  10. The effect of humidity on engine power is considered.

  11. The Primary Flight Display (PFD) and standby instruments show values of calibrated airspeed, Mach number, and pressure altitude which have been corrected for in-flight position errors within the Air Data System (ADS). In-ground position error is negligible.

  12. Minimum brake operating pressure of 3000 PSI (20,700 kPa).

  13. For negative pressure altitudes, use sea level data on all performance charts.

VEF, CRITICAL ENGINE FAILURE SPEED - the airspeed at which either engine fails.

V1, TAKEOFF DECISION SPEED - the speed from which a decision to continue the takeoff results in a takeoff distance that will not exceed the available accelerate-go distance, or from which a decision and action to bring the airplane to a full stop will not exceed the accelerate-stop distance available. In the event of an engine failure, this speed takes account of the pilot recognition and reaction time of 1.0 seconds, including the pilot’s first action after recognizing the engine failure. For an all-engine rejected takeoff, this is the speed at which the pilot performs his first action to abort. More about this: Technical / V1.

VR, ROTATION SPEED - the speed at which rotation to the takeoff attitude is initiated.

V1/VR, TAKEOFF DECISION SPEED RATIO - the ratio of the takeoff decision speed, V1, to the rotation speed, VR.

V2, TAKEOFF SAFETY SPEED - the target speed to be attained at the 35 foot height following an engine failure. More about this: Technical / V2.

VSE, EN ROUTE CLIMB SPEED - the recommended airspeed for single-engine climb in the en route (clean) configuration.

Reference zero occurs at 35 feet on a dry runway, 15 feet on a wet runway. (14 CFR 25 §25.111 and 14 CFR 25 §25.113)

Figure: Reference zero, from G450 Airplane Flight Manual §5.1, pg. 5.1-5.

Maximum demonstrated crosswind for takeoff and landing is 24 knots.

Takeoff is based on aircraft line up on the runway, brakes set, power at takeoff setting, brakes released, and the aircraft accelerated to V1 with both engines operating.

Takeoff abort is based on no reverse with a dry runway, one or both engines at reverse with a wet runway.

When is a Runway Contaminated?

[G450 Airplane Flight Manual §5.1] The runway is considered contaminated when more than 25% of the runway surface area (whether in isolated areas or not), within the required length and width being used, is covered by surface water more than 0.125 inch (3 mm) deep, or by slush or loose snow equivalent to more than 0.125 inch (3 mm) of water.

When is a Runway Wet?

[G450 Airplane Flight Manual §5.1] A runway is considered wet when it is well soaked (there is sufficient moisture on the runway surface to cause it to appear reflective) but without significant areas of standing water.

Flex Takeoff Thrust Limitations

[G450 Airplane Flight Manual, Appendix A, § 1]

  1. FLEX takeoff thrust may be used on dry or wet, hard-surfaced runways, and the takeoff performance computed in this Appendix is limited to takeoffs for nil or uphill runway slopes and no wind or headwind conditions, only. (FLEX thrust cannot be used for takeoffs with tailwind or downhill slope; the AFM or TOLD must be used to properly compute takeoff performance for these conditions.)
  2. FLEX EPR takeoff thrust procedures are prohibited on runways contaminated with standing water, snow, slush, or ice. A contaminated runway is a runway where more than 25 percent of the required field length is covered by standing water or slush more than 0.125 inches (3.2 mm) deep, or that has an accumulation of snow or ice.
  3. Use of Wing Anti-icing bleed is not approved.
  4. The Anti-Skid Brake System must be ON and operating.
  5. The Auto Ground Spoilers must be operative when using 10° flaps for takeoff.
  6. All rated takeoff EPR limitations must be observed.
  7. To ensure that at least 75% of rated takeoff thrust is used and that takeoff configuration warnings are not inhibited, FLEX power settings must not be less than rated EPR levels provided in the FLEX tables.
  8. Both engines must be capable of developing rated takeoff EPR. To check for a deteriorated engine, at least one rated EPR takeoff is required every 100 flights or 100 flight hours, whichever occurs first.
  9. This Appendix does not include any obstacle clearance information. Check obstacle clearance using the charts presented in the Airplane Flight Manual for the selected takeoff flap setting and the assumed temperature. If obstacles are not cleared, decrease the assumed temperature by columns until obstacle clearance has been obtained. New V-speeds and FLEX EPR must then be determined.

1. Dry or Wet runway (Rated or Flex), 10° or 20° Flaps

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-30] The pilot can select one of the three methods listed below to complete performance initialization.

  • Full Performance - The FMS uses an uploaded and learned aircraft database file to perform time and fuel calculations. The time calculations are also based on pilot-entered speed schedules and winds. Computed cruise speed schedules such as long range cruise (LRC) and maximum speed can be selected.
  • Pilot Speed/Fuel Flow - The FMS uses pilot-entered speed schedules and winds to perform time calculations. The fuel calculations are based on pilot-entered cruise fuel flow. Adjustments are made for the higher fuel flow in climb.
  • Current Ground Speed/Fuel Flow - The fuel calculations are based on the current fuel flow displayed on the FUEL MGT page. If a fuel flow entry is made on that page, it takes the place of the sensed fuel flow. The time calculations are based on the current groundspeed.

Unless you have a database problem, you should see "Full Performance" here. Selecting "Pilot Speed/Fuel Flow" or "Current Ground Speed/Fuel Flow" turns your FMS into one of the earliest G-III flight management systems which always started a flight saying you didn't have enough gas because it didn't understand fuel flows change as the flight progresses.

The easiest method begins with down linking and activating a flight plan. This lets the performance computer know which airport to use and makes the performance initialization pages that much smarter. Once that is done, select PERF > PERF INIT.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 12] The climb and descent speed schedules are always displayed as both a calibrated airspeed (CAS) and a MACH. Changes can be made by entering a CAS, a MACH, or both separated by a slash (/). The leading slash (/) is used as an option when entering a MACH only. Entering *DELETE* returns the default climb or descent speed schedule. The FMS always uses the CAS or MACH entry that provides the lowest TAS at the current altitude.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 12] The cruise speed schedule can be a CAS/MACH pair, only CAS, only MACH, or a system-generated cruise speed schedule. Entries of a CAS, a MACH, or both are accepted. Entering *DELETE* returns the default cruise speed schedule which is LRC in FULL PERF and the value from the aircraft database (or 300/.80) in CURRENT GS/FF or PILOT SPD/FF. The two other system-generated schedules, MAX SPD, MAX END and MXR SPD, can be selected on the CRUISE MODES page only. If both a CAS and MACH are entered, the active speed command is the CAS or MACH that provides the lowest TAS at the current altitude. If the LRC or MAX SPD schedules are active, the speed command is issued as a MACH at higher altitudes and a CAS at lower altitudes. This is determined by the VMO/MMO crossover altitude. If the cruise speed schedule is MAX END, the speed command is always CAS.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 13] In addition to the speed entries, a default descent angle can be entered in this field. If the angle is being entered independent of the speed entries, the angle can either be entered directly or with two leading slashes (//).

You will probably want to change CRUISE to 300/0.80M or 300/0.83M. It will retain this default but occasionally finds its way back to LRC. Unless you are in the northeast U.S., you may find selecting a descent angle of 2.5° will make for smoother descents. (See G450 Performance-Descent for an explanation of why.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 19] Entries for step increment must be in thousands of feet. The three trailing zeros can be omitted. Entering *DELETE* returns the selection to no step or zero feet. Step climbs are used for long range flights to optimize the aircraft performance. As the aircraft burns fuel, the optimum altitude goes up. If a step increment is selected, the FMS computes the bottom of step climb (BOSC) point. The BOSC is where the aircraft is light enough to climb by the amount of the step increment to a new cruise altitude. More than one step climb can be calculated for a flight. When a step increment is selected, time and fuel predictions assume that the step climbs will be made. Therefore, a step increment should only be selected when the intent is to make the step climbs. If clearance is not given or the step climb is not going to be made, step increment should be set to zero in order to maintain accurate time and fuel predictions.

You can rarely count on step climbs as the FMS computes them so you normally leave this field as zero. For very long flights at the maximum range of the aircraft, it may be useful to enter a step climb to avoid an insufficient fuel message.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 19] The method of calculating fuel reserve. Entering *DELETE* returns to the default reserve mode which is National Business Aircraft Association (NBAA) rules.

The NBAA rules include the fuel required to fly from the destination to the alternate plus 30 minutes of holding at 5,000 feet at the alternate. If the distance to the alternate is less than 200 nm, 200nm is used.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 19] The default values of takeoff/landing fuel (TO/LDG FUEL) are supplied from the aircraft database. However, manual entries can be made. Manual entries are saved for the next flight. Entering *DELETE* returns the default values.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 21] The transition altitude can be entered here. The FMS uses the input to determine how to display altitudes. Altitudes above the transition altitude are displayed as flight levels (FL) and below in feet. Entering *DELETE* returns the default value of 18,000 feet.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 21] Speed limits associated with altitudes, not waypoints, can be entered. For U.S. operation, 250 knots below 10,000 feet is entered. The FMS speed command is limited to this speed below the restriction altitude. Entering *DELETE* removes the speed/altitude limit and displays dashes. This is the only field that can be left with dashes and still allow performance data to be computed.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 21] The initial cruise altitude is entered at this location. The FMS uses the initial cruise altitude to determine the altitude where the cruise phase of flight commences. The FMS changes the speed command and EPR rating from climb to cruise when the aircraft levels at the initial cruise altitude or higher. The default for INIT CRZ ALT is OPTIMUM if the performance mode is FULL PERF. The FMS calculates the optimum cruise altitude based upon the performance initialization data. After performance initialization is completed, the calculated optimum altitude is displayed in small characters on this page.

The initial cruise altitude determines when the performance computer directs cruise flight to begin and therefore when CLB thrust switches to CRZ thrust. The default value of OPTIMUM is typically close to ceiling altitude and is almost never of any use when flying in an ATC environment.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 22] The forecast temperature deviation at the cruise altitude can be entered in this field. The deviation is relative to the International Standard Atmosphere (ISA). If no entry is made, the displayed default of zero is used. Do not input the temperature deviation at the field elevation. Temperature impacts most performance predictions: the climb gradient, the ceiling altitude, the fuel consumption, the groundspeed predictions, and more.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 23] An average cruise wind and corresponding altitude can be entered at 3L and 3R. No entry is required, but it is recommended. If no entry is made, the FMS assumes zero wind. When the cruise wind is entered at 3L, prompts are displayed at 3R. The altitude must also be entered before the cruise wind is accepted. Entering *DELETE* returns the default value of zero.

Entering a temperature deviation and cruise winds will erase any leg entries if you uploaded them. You should either upload leg winds and temperatures or cruise values here.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-30 ¶1, Page 23] Basic operating weight (BOW) is retained in memory but it should be verified on each flight. A new entry can be made at any time. Entering *DELETE* returns the entry prompts. The fuel weight,when sensed by the fuel quantity system, is displayed in small characters. The pilot can manually enter a fuel weight which is displayed in large characters. Cargo weight and passenger count must be entered in order to compute performance data. The average weight per passenger can also be adjusted by entering a slash (/) followed by the weight (e.g., /200). When performance initialization is complete, the CONFIRM INIT prompt is displayed in the lower right corner of this page. The CONFIRM INIT prompt must be selected for the performance function to calculate performance data and for the VNAV function to be available. Selecting the CONFIRM INIT prompt displays the PERF DATA page. After confirming initialization, the prompt at 6R of the PERFORMANCE INIT page becomes PERF DATA on all PERF INIT pages.

The PERF DATA pages have some useful information but if you've done everything else right, you really don't need to visit the three PERF DATA pages:

Figures: PERF DATA, from G450 Aircraft Operating Manual §2B-26-40, Figures 18, 19, 20.

Where you need to go now is TO INIT...

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 33] The FMS continuously performs a takeoff configuration check. This check compares the initialization inputs/selection against actual aircraft or environmental conditions. The following items are included in the configuration check:

  • Pressure altitude (within 100 feet of sensed)
  • Baro setting (within 0.10 inches of Mercury)
  • Anti-skid
  • Spoilers
  • Flaps
  • Anti-ice
  • Takeoff weight (within limits)

You don't need to make any entries on this page, only check it if things go wrong later on.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 36]

  • The selected runway identifier is displayed. If no runway has been selected on the DEPARTURE pages, the field displays dashes. Entries are permitted and can be made using the 2-digit identification (e.g., 29 meaning 290°).Entries in degrees require a 3-digit input. The available runway length and its magnetic heading is displayed. If no runway has been selected, entry prompts are displayed. An entry of runway length can be made to override the database information or supply the length when the runway is not in the database. Note that the actual takeoff and landing length of a runway can differ from the FMS database due to displaced threshold, stopway, or temporary relocated threshold.
  • The FMS computed slope of the runway is displayed. The FMS computes the slope by taking the elevation of the far end of the runway minus the elevation of the near end of the runway and dividing by the runway length. Positive slopes are shown with an up arrow (↑). Negative slopes are shown with a down arrow (↓). If no runway has been selected, entry prompts are displayed. An entry of slope can be made to override the database information or supply the slope when the runway is not in the database.
  • The runway width, if available from the database, is displayed. An entry for displaced threshold can be made on this line. The default displaced threshold entry is 31 meters or 100 feet.
  • An entry for runway clearway and stopway can be entered on these lines. The clearway is used in computing the available runway for accelerate and go. The stopway is used in computing the available runway for accelerate and stop. The stopway distance from the navigation database is displayed as the default value. The clearway default value is zero meter.
  • The sensed static air temperature is displayed in this field. Under normal circumstances, the sensed temperature should be used. However, an entry can be made for cases where the predicted temperature for takeoff is different than the current sensed temperature. An entry can be made in degrees Celsius. Entries in degrees Fahrenheit require a leading slash (/).
  • The surface wind is a required entry on this page.
  • The computed pressure altitude and barometric (BARO) setting are displayed on this line. Also displayed is the runway elevation from the database. While entries are permitted for all these items, no entries are normally made. The only recommended entry is elevation in the case where the runway is not in the database. Entry of BARO setting is permitted and can be made in inches of mercury or millibars. Use *DELETE* to return to the default value and units. When a runway has been selected, the pressure altitude is computed based on the field elevation and the BARO setting. If an entry of pressure altitude is made, elevation is computed using the BARO set.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 37] An entry of obstacle distance from the departure end of the runway and elevation can be made on these lines. The default is NONE. Depending upon the configuration, obstacle distance entries can be in either feet, meters or nautical miles. Entries in nautical miles require a leading slash (/).

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 37] An entry of a standard instrument departure (SID) gradient in FT/NM, from the departure end of the runway, and elevation in FT MSL is made on this line. The default is NONE.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 38] Obstacle distance is referenced from the departure end of the runway. The departure end of the runway for obstacle distance is defined to be the end of the runway at which the aircraft is at altitude. It is NOT the runway end at which the throttles are advanced for takeoff. Some departures specify obstacle clearance in terms of a minimum rate of climb or climb gradient. Unless that requirement can be related to a specific obstacle at a given distance, the FMS does not accept either of these minimum values. This is because the FMS is basing its obstacle clearance on the computed takeoff field length which is different than the runway length.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 38] An entry of SID runway gradient and elevation can be made on these lines. Depending on the configuration, SID gradient entries can be in either feet or nautical miles. Entries in nautical miles require a leading slash (/).

I've looked at this over and over again and think the note that says "Some departures . . . the runway length" would have been less confusing had it said: "If your obstacle is specified in terms of a minimum climb rate, enter it under SID instead." The Aspen LINDZ FIVE departure, for example, says this: "Rwy 33: 400-1 with minimum climb of 460' per NM to 14000'." I would enter 460 with LSK 5L and 14000 with LSK 5R.

The FMS is basing its decisions on the aircraft losing and engine at V1 which isn't necessarily how you want to base your go/no-go criteria. See Departure Obstacle Avoidance for methods of increasing your allowable payload safely.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 38]

  • The selected engine bleeds setting for takeoff calculations is displayed at 1L. The default setting is OFF. Select the OR prompt at 1R to select other bleed settings. If the actual engine bleeds setting is different than the selected setting, this line is displayed in inverse video.
  • The selected spoiler setting for takeoff calculations is displayed at 3L. The default setting is OPERATIVE (auto spoilers). The setting can be changed at 3R to INOP (manual spoilers). If the actual spoiler setting is different than the selected setting, this line is displayed in inverse video.
  • The selected anti-skid setting for takeoff calculations is displayed at 4L. The default setting is OPERATIVE. The setting can be changed at 4R. If the actual anti-skid setting is different than the selected setting, this line is displayed in inverse video.
  • The selected runway condition for takeoff calculations is displayed here. The setting can be changed at 5R. The default is DRY.

See G450 Procedure & Techniques / Takeoff for a handy pneumonic about how to know what to check the next time you are at the end of the runway without boxed numbers.

Photo: From Haskel's cockpit.

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 39]

  • The BTMS configuration is displayed at this line (1L and 1R). When ENABLED, brake temperature computations are used in computing the TAKEOFF DATA. When DISABLED brake temperature computations are not used in computing the TAKEOFF DATA. The default is ENABLED. Should the FMS not be able to perform brake temperature monitoring computations, ENABLED is displayed in inverse video.
  • The selected thrust mode for takeoff calculations is displayed at 2L. The default setting is RATED EPR. Select 2R to change the setting. RATED EPR is defined in the AFM as using full takeoff thrust. The FMS calculates takeoff data for the available field length based on the takeoff EPR rating and V1 between V1MAX and V1MIN on the TAKEOFF DATA pages. FLEX is defined in the AFM as reduced takeoff thrust. This power setting is calculated observing all the limitations in the AFM. The FMS calculates takeoff data for the available field length based on reducing EPR as much as possible (but not more than 0.154 EPR less than RATED EPR, and not less than 1.39 EPR). The pilot can select any V1 between V1MAX and V1MIN on the TAKEOFF DATA pages.
  • The selected flap setting for takeoff calculations is displayed at 3L. The default setting is 20°. The setting can be changed at 3R. If the actual flap setting is different than the selected setting, this line is displayed in inverse video.
  • The takeoff gross weight is displayed on this line (4L). The takeoff weight is the gross weight from PERF INIT page 5. An overriding manual entry is permitted on this page. The default takeoff weight can be restored by entering *DELETE*. If the PERF INIT weights have not been entered, the T.O. WEIGHT line displays a prompt. If the weight changes during ground operations, the takeoff data is automatically calculated using the new weight unless a weight has been manually entered.
  • The CONFIRM INIT prompt is displayed when all required takeoff initialization items are entered. The CONFIRM INIT prompt must be selected to start takeoff data calculation. Changes made to takeoff initialization after selection of the CONFIRM INIT prompt are automatically recalculated without selecting CONFIRM INIT. In other words, selection of the CONFIRM INIT prompt is only required for initial calculation.

If the BTMS becomes confused or simply forgets what time it is, it will not be able to assure the performance computer that the brakes are okay and you will not get boxed V-speeds. If you know the brakes are not hot, simply disable the BTMS and the speeds will box. The BTMS will learn the date and record the next peak temperature and everything will be okay again.

Once you've hit the CONFIRM INIT you should get takeoff data on the display controller and takeoff data on the MCDU.

Figure: Takeoff Data, from G450 Aircraft Operating Manual §2B-26-00, Figure 30.

Other Methods

You can use other methods to compute takeoff data if you wish, say you are planning the trip and don't happen to have a performance computer handy:


2. Manual Data

Figure: Takeoff Planning Example, from G450 Airplane Flight Manual Appendix A, Figure A-1.

You would never do this, you say? Well, the only time I ever do it is during an oral. So here goes:

[G450 Airplane Flight Manual §Appendix A] Appendix A of the AFM provides tabular charts that provide a mechanism to using the assumed temperature method to find FLEX, reduced thrust takeoff data. To compute flex data using Appendix A:

  1. Start with the gross weight in the left column.
  2. Follow the row to the right column under the ambient temperature.
  3. The FLD LNGTH shows how much runway you will need using rated thrust.
  4. Follow the FLD LNGTH row to the left until you have run out of runway, then go one column to the right so that you have more runway than FLD LNGTH required.
  5. Below that number you will find V1, VR, and V2. To the left you will find VSE, and VREF. To the top you will find FLEX EPR.

You can also use AFM, Appendix A to find reduced thrust data for wet runways. The method is identical to the one listed above for dry runways, just make sure you are looking at the correct tabular chart - the one that says "WET RUNWAY" at the top left. Once you get the numbers, you will have to manually input them into the display controller.


3. Obstacles

What you should really do here is download the applicable data from a qualified airport analysis program. More on this: Departure Obstacle Avoidance. But if you don't have that, the performance computer can help. Using Runway 08 at Garfield County Regional, Rifle, Colorado, as an example, we can learn the following from the EDUKY THREE Departure:

  • Airport elevation: 5537'
  • Lower than standard weather minimums available if you can climb 396' per NM to 11100'
  • Four obstacles are given, three of which appear pertinent:
    • 452' from DER, 5551' MSL
    • 4024' from DER, 5642' MSL
    • 1.7 NM from DER, 5969' MSL

Photo: From Haskel's cockpit.

You should start the evaluation by inserting your desired fuel, it might work.

Photo: From Haskel's cockpit.

Then enter the obstacle data. For the sake of this example, we will leave out the SID climb gradient for now. Note that in the case of the third obstacle, you can enter the 1.7 NM distance with a leading slash; "/1.7" to have the performance computer do the conversion to feet for you.

Photo: From Haskel's cockpit.

You may be greeted with a "TAKEOFF OUT OF LIMITS" message and the PERF DATA page showing you the performance computer's best guess on what your maximum weight should be. In the case, it is around 1,200 pounds less.

Photo: From Haskel's cockpit.

For our example, we will reduce our fuel by 2,000 lbs.

Photo: From Haskel's cockpit.

Now we are presented with valid takeoff data, but this just shows us we can make it off the ground. Will we beat the obstacles?

Photo: From Haskel's cockpit.

Our highest obstacle is 5,969' and we appear to have beaten that. But the SID also called for a minimum climb gradient of 396' per NM to 11,100'. The performance computer shows us falling well below that. (More about what the difference between the obstacle distance/height versus the climb gradient down below.)

Photo: From Haskel's cockpit.

Now if we enter the SID climb gradient, the performance computer once again says "TAKEOFF OUT OF LIMITS"

Photo: From Haskel's cockpit.

We can repeatedly lower our fuel until the message stops repeating itself. Here we see 20,000 pounds is still too much.

Photo: From Haskel's cockpit.

At 12,400 pounds of fuel the performance computer is again happy.

Photo: From Haskel's cockpit.

So what do these numbers mean?

[G450 Aircraft Operating Manual §2B-26-50 ¶3, Page 43]

  • 1L -- The minimum gross Level Off height from reference zero is displayed here.
  • 1R -- The minimum Level Off altitude (altimeter indicated) is displayed here.
  • 2L -- The minimum gross gradient from reference zero is displayed here.
  • 2R -- The minimum SID gross gradient from DER is displayed here.
  • 3L -- The maximum gross Level Off height from reference zero is displayed here. This value is based on a 10-minute limit on the use of takeoff thrust for single engine operation.
  • 3R -- The maximum Level Off altitude (altimeter indicated) is displayed here.
  • 4L -- The average gross gradient from reference zero is displayed here.
  • 4R -- The maximum SID gross gradient from DER is displayed here.
  • 5L -- From reference zero, note - an * indicates that the data is computed from the Reference Zero position on the runway.
  • 5R -- From DER, note - ** indicates that the data is computed from the departure end of the runway (DER).
  • REF ZERO, the left column, refers to performance from the point where the aircraft leaves the ground. All of the heights are AGL.
  • DER, the right column, refers to performance from the departure end of the runway. All of the altitudes are MSL.

Minimum versus maximum level off?

[G450 Performance Handbook Page 5.6-3] The minimum level-off height is 1500 feet AAL. When multiple obstacles exist in the takeoff profile, the highest obstacle will dictate the minimum level-off height even if this is not the most demanding obstacle from a required gradient standpoint. If the horizontal distance is more than 120,000 feet from Reference Zero, the recommended level-off altitude must be determined as the sum of the obstacle height above Reference Zero plus the product of .008 times the horizontal distance from Reference Zero.

[G450 Performance Handbook Page 5.6-3] The maximum level-off height that can be used is also presented on the Distant Obstacle Clearance chart. The maximum level-off height is determined at the intersection of the net 10-minute limit line with the available Reference Climb Gradient line. This limit line was established to ensure that the total time to accelerate from brake release to V2 after recognizing an engine failure at V1 and then climb at V2 with flaps down to the maximum level-off height does not exceed 10 minutes (the engine-out time limit on use of Takeoff Thrust). For example, if the available Reference Climb Gradient is 10.0%, the maximum level-off height is determined from the diagonal Gross Height lines to be about 9000 feet at the intersection of the 10.0% gradient line and the net 10-minute limit line.

[G450 Performance Handbook Page 5.6-4] If the true aircraft altitude is below the Transition Altitude (altitude at which the altimeter barometric scale is set to 29.92 inches of Hg), the target level-off altitude will be equal to the airport elevation plus the pressure altitude increment determined above. If the true aircraft altitude is at or above the Transition Altitude, the target altitude will be the pressure altitude increment determined above plus the higher of the airport elevation or the airport pressure altitude. Note that for ISA-day temperatures, the pressure altitude increment equals the gross height increment. A temperature deviation less than ISA will yield a pressure altitude increment that is greater than the gross height increment, while a temperature deviation greater than ISA will yield a pressure altitude increment that is less than the gross height increment.

Figure: Min versus Max Level Off, from Haskel's Notebook.

Why is min level off rate (ft/nm) usually a higher number than the max level off rate? Both minimum and maximum level offs are the exact same flight path but one ends before the other. The minimum level off altitude ends as soon as the aircraft reaches either 1,500' above the airport or clears all obstacles. The maximum level off altitude ends at 10 minutes, the single engine time limit. Since the maximum level off occurs later, you will be higher and your average climb rate will be lower. Both altitudes are corrected for temperature and pressure deviation from 29.92.

Photo: From Haskel's cockpit.

Once all this is done, you should have good V-speeds in the display controller . . .

Photo: From Haskel's cockpit.

Figure: Airport Analysis KRIL, from Departure Obstacle Avoidance.

Remember the note about Airport Obstacle Analysis? Had you used it, you could have departed using the same departure procedure at 62,491 lbs, 6,000 lbs heavier. Use a tailored procedure and you can go even heavier. How is this possible? See: Departure Obstacle Avoidance.


4. Contaminated Runway (Certain Conditions)

Figure: Takeoff Performance Water Depth Less than 5mm, from G450-OIS-2, Table 24c.

While the AFM provides charts for wet or dry runways, it does not consider contaminated runways. Of course that means the performance computer is lost too. The Performance Handbook does have graphical charts that are a bit cumbersome and mimic the procedures given below under Contaminated Runway (Other Conditions), which uses G450 OIS-02, Section B. The next section in that OIS, Section C, provides tabular data under certain conditions:

[G450-OIS-2 § C]. Tabular takeoff data are contained for the following 4 contaminant types and/or depths:

  • Compacted snow (Tables 1c-11c);
  • Ice (Tables 12c-22c); standing water, slush or loose snow (Tables 23c-33c) with the equivalent water depth between 3 mm (0.12 in.) and 5 mm (0.2 in.); and
  • Standing water, slush or loose snow (Tables 34c-44c) with the equivalent water depth between 5 mm (0.2 in.) and 15 mm (0.6 in.).

Separate tables are presented for different pressure altitudes, and at each pressure altitude, the tabular data are a function of aircraft weight and temperature. The lack of data at higher weights and temperatures indicate conditions where performance is restricted by climb limits, brake energy limits or tire speed limits. For a given weight, altitude, temperature, contaminant type and RSC depth, the Section B and Section C data may not be in exact agreement as the Section B graphical data does contain additional conservatism that is not included in the Section C tabular data.

This is easy, you just need to make sure you are on the right chart. The example shown here is for standing water, slush, and loose snow with an equivalent water depth of less than 5 mm; 1000' pressure altitude, and 20° flaps. There are also charts for compacted snow and ice and for equivalent water depths up to 15 mm.

Figure: Equivalent Depth for Slush / Loose Snow, from G450-OIS-2, Table 1a.

If you are dealing with compacted snow or ice, just turn to the appropriate page. If you are dealing with slush or loose snow, you need to convert that to an equivalent water depth using Table 1a:

At this point you look for the correct chart, either ≤5 mm V1 < VR or 5 mm to 15 mm V1 = VR. Once you've done that, there is a graphical chart to makes corrections for anti-ice, wind, and runway slope. As long as you get the right chart, the rest should be easy.

So what is the draw back? The charts are set up for even thousands of feet pressure altitude and four thousand pounds of gross weight. You may find using the graphical charts yields a higher grossest. I say might because the OIS does say the graphs are more conservative.


5. Contaminated Runway (Other Conditions)

Section B of the G450-OIS-2 provides graphical data for takeoff on contaminated runways.

While straightforward, chasing through the lines offers multiple chances of error. You should try the tables shown above, Contaminated Runway (Certain Conditions) first, but fear not the following process.

Figure: Equivalent Depth for Slush / Loose Snow, from G450-OIS-2, Table 1a.

Convert slush to an equivalent depth of standing water using OIS-2 Table 1a, also reproduced here:

Figure: Equivalent Depth for Slush / Loose Snow, from G450-OIS-2, Table 1b.

Enter the Effective Runway Length (ERL) Required chart with temperature and gross weight to determine the Effective Runway Length, Figure 1b, also reproduced here:

Figure: Equivalent Depth for Slush / Loose Snow, from G450-OIS-2, Table 3b.

Enter the bottom of the ACCELERATE-STOP DISTANCE chart (figure 3b) with the runway length, the RSC depth, and the other entries to determine a reference accelerate-stop distance.

Figure: Equivalent Depth for Slush / Loose Snow, from G450-OIS-2, Table 4b.

Enter the bottom of the ACCELERATE-STOP GO chart (figure 4b) with the runway length, the RSC depth, and the other entries to determine a reference accelerate-stop distance.

Figure: Equivalent Depth for Slush / Loose Snow, from G450-OIS-2, Table 2b.

Enter the RUNWAY LENGTH AND V1 ADJUSTMENTS chart (figure 2b) with the ERL, reference accelerate-go, and reference accelerate-stop. Read the V1/VR ratio.

With an RSC between 3 mm and 5 mm, the V1/VR ratio must be between 0.80 and 1.00. With an RSC above 5 mm, the V1/VR ratio must be 1.00.

If the V1/VR ratio is too low, adjust the reference accelerate-go distance downward and the reference accelerate-stop distance upward along the ERL line.


Other Issues: Flex versus Rated

It used to be said you could divide Gulfstream pilots into two factions: those who flex and those who don't. First, lets cover the rules and then some rationale for flexing.

[G450 Airplane Flight Manual §Appendix A §1]

  1. FLEX takeoff thrust may be used on dry or wet, hard-surfaced runways, and the takeoff performance computed in this Appendix is limited to takeoffs for nil or uphill runway slopes and no wind or headwind conditions, only. (FLEX thrust cannot be used for takeoffs with tailwind or downhill slope; the AFM or TOLD must be used to properly compute takeoff performance for these conditions.)
  2. FLEX EPR takeoff thrust procedures are prohibited on runways contaminated with standing water, snow, slush, or ice. A contaminated runway is a runway where more than 25 percent of the required field length is covered by standing water or slush more than 0.125 inches (3.2 mm) deep, or that has an accumulation of snow or ice.
  3. Use of Wing Anti-icing bleed is not approved.
  4. The Anti-Skid Brake System must be ON and operating.
  5. The Auto Ground Spoilers must be operative when using 10° flaps for takeoff.
  6. All rated takeoff EPR limitations must be observed.
  7. To ensure that at least 75% of rated takeoff thrust is used and that takeoff configuration warnings are not inhibited, FLEX power settings must not be less than rated EPR levels provided in the FLEX tables.
  8. Both engines must be capable of developing rated takeoff EPR. To check for a deteriorated engine, at least one rated EPR takeoff is required every 100 flights or 100 flight hours, whichever occurs first.
  9. This Appendix does not include any obstacle clearance information. Check obstacle clearance using the charts presented in the Airplane Flight Manual for the selected takeoff flap setting and the assumed temperature. If obstacles are not cleared, decrease the assumed temperature by columns until obstacle clearance has been obtained. New V-speeds and FLEX EPR must then be determined.

Those who don't flex say they don't want to give up the performance, citing the "Runway Behind You" maxim. Me? I flex whenever I can as often as I can. You are giving up a maximum of 25% of the thrust and I always ensure I have at least 2,000 feet of runway to spare. (If not, go into the runway available page of the performance computer and shorten the runway artificially, the performance computer does the rest. What if you lose an engine at V1? The data assumes you will and have a little less thrust makes directional control easier.


Other Issues: Flaps 20 versus 10?

The numbers are not cut and dried but generally speaking, going from 20° to 10° flaps costs you about 7% runway distance at heavy weights (down to less than 1% at lower weights), but gives you about 7% better climb rate at lower weights down to just 2 or 3% at higher weights.

Is that important? We worried about this in the G-III because we had to. I've never opted for less than 20° of flaps in the G-IV, G-V, or G450. There was never a need.


Other Issues: Anti-ice ON versus OFF?

In older Gulfstreams we often took off with the anti-ice off until leaving the ground so as not to lose the performance. The penalty for using anti-ice in the G450 isn't nearly as much as it was in the G-IV. The most it ever costs you to use both cowl and wing anti-ice is 400' in accelerate-go distance. So you might as well use it, eh?


References

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

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

Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013

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

Gulfstream G450 Performance Handbook, GAC-AC-G450-OPS-0003, Revision 20, November 30, 2011