Figure: Climb gradient summary, from Eddie's notes.

Eddie Sez:

By virtue of pure luck, kismet, and serendipity, I started my big airplane experience flying the original version of the KC-135 tanker, a 300,000 pound monstrosity powered by four tiny 9,000 pound thrust engines. The airplane taught the importance of energy management during all phases of flight and learning to cross obstacles to "scrape paint" because that's all you could do.

In the civilian world we have to do better than scrape paint. For a discussion of obstacle climb performance see Departure Obstacle Avoidance. Even without an obstacle, 14 CFR 25 requires our U.S. certified aircraft be able to make certain climb minimums, as shown below.

What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue. Don't sweat all the legaleeze in the FAR, the drawing shown above says everything you need to know. Most Gulfstream pilots have it even better, as we don't have third and final segments to worry about.

Minimum Climb Performance

[14 CFR 25§25.101(f)] Unless otherwise prescribed, in determining the accelerate-stop distances, takeoff flight paths, takeoff distances, and landing distances, changes in the airplane's configuration, speed, power, and thrust, must be made in accordance with procedures established by the applicant for operation in service.

[14 CFR 25§25.105(a)(2)] In icing conditions, if in the configuration of §25.121(b) with the takeoff ice accretion defined in appendix C:

(i) The stall speed at maximum takeoff weight exceeds that in non-icing conditions by more than the greater of 3 knots CAS or 3 percent of VSR; or

(ii) The degradation of the gradient of climb determined in accordance with §25.121(b) is greater than one-half of the applicable actual-to-net takeoff flight path gradient reduction defined in §25.115(b).

[14 CFR 25 §25.111] Takeoff path.

(a) The takeoff path extends from a standing start to a point in the takeoff at which the airplane is 1,500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and VFTO is reached, whichever point is higher. In addition—

(1) The takeoff path must be based on the procedures prescribed in §25.101(f);

(2) The airplane must be accelerated on the ground to VEF, at which point the critical engine must be made inoperative and remain inoperative for the rest of the takeoff; and

(3) After reaching VEF,the airplane must be accelerated to V2.

(b) During the acceleration to speed V2, the nose gear may be raised off the ground at a speed not less than VR. However, landing gear retraction may not be begun until the airplane is airborne.

(c) During the takeoff path determination in accordance with paragraphs (a) and (b) of this section—

(1) The slope of the airborne part of the takeoff path must be positive at each point;

(2) The airplane must reach V2 before it is 35 feet above the takeoff surface and must continue at a speed as close as practical to, but not less than V2, until it is 400 feet above the takeoff surface;

(3) At each point along the takeoff path, starting at the point at which the airplane reaches 400 feet above the takeoff surface, the available gradient of climb may not be less than—

(i) 1.2 percent for two-engine airplanes;

(ii) 1.5 percent for three-engine airplanes; and

(iii) 1.7 percent for four-engine airplanes.

(4) The airplane configuration may not be changed, except for gear retraction and automatic propeller feathering, and no change in power or thrust that requires action by the pilot may be made until the airplane is 400 feet above the takeoff surface; and

(5) If §25.105(a)(2) requires the takeoff path to be determined for flight in icing conditions, the airborne part of the takeoff must be based on the airplane drag:

(i) With the takeoff ice accretion defined in appendix C, from a height of 35 feet above the takeoff surface up to the point where the airplane is 400 feet above the takeoff surface; and

(ii) With the final takeoff ice accretion defined in appendix C, from the point where the airplane is 400 feet above the takeoff surface to the end of the takeoff path.

14 CFR 25.111 does not mandate the first, second, third, and final segment nomenclature but does mandate minimum climb performances for these segments at the noted altitudes:

Minimum Climb Performance
Engines 1st Segment 2nd Segment 3rd Segment Final Segment
2 Engine Positive 2.4% Positive 1.2%
3 Engine 3.0% 2.7% Positive 1.5%
4 Engine 5.0% 3.0% Positive 1.7%

Table: Climb gradient summary, from Eddie's notes.


Figure: Obstacle and SID parameters, from G450 Airplane Flight Manual, §5.6, page 5.6-1.

[G450 Airplane Flight Manual, §5.6.]

  • The obstacle clearance procedure is to climb with landing gear retracted, flaps in takeoff position at a speed of V2 to at least 1500 feet above the takeoff surface.
  • 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.
  • 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).

The Gulfstream III, IV, V, 450, and 550 meet the 14 CFR 25 requirements by maintaining second segment performance beyond 1500 feet, eliminating the third and final segments. V2 is flown from 35 feet to at least 1500 feet, which will achieve the 2.4% second segment climb requirement and exceed the required third and final segment minimums. The recommended level off height is a function of the obstacle height and the horizontal distance from reference zero. It is further limited by the operating time on the operating engine at takeoff thrust. This limit is five minutes on the G-III and ten minutes on the G-IV, V, 450, and 550. [AFMs Section 5.6]

Figure: VFS, from G450 Aircraft Operating Manual, §2B-05-30, ¶1.D. page 12.

[G450 Aircraft Operating Manual, §2B-05-10, page 12.] VFS is not displayed unless it is set through the aircraft personality module (APM) options.

[G550 Aircraft Operating Manual, §2B-05-30, ¶1.D, page 12.] VFS is not displayed unless it is set through the aircraft personality module (APM) options.

[GV Aircraft Operating Manual, §2B-02-20, ¶5.H, page 29.] For aircraft with JAA certification, VFS is not displayed on the FLT REF menu.

While VFS is defined for the G-III, G-IV, V, 450, and 550 as 1.25 times VSO, it is not used procedurally in the G-IV, V, 450, or 550. In those aircraft, takeoff with an engine failed passed V1 calls for flying from V2 to VSE. The entry will be blank on G-V aircraft with JAA certification. The entry will appear in the G-IV and non-JAA G-Vs, but it is shown for information purposes only and is not used procedurally.

Other Aircraft (for comparison).

Figure: Takeoff Flight Path (Gross Level Off Height Less than 1500 Feet), from CL604 Aircraft Flight Manual, §06-04-2.

Many aircraft require an intermediate level off prior to 1,500' to clean up and accelerate. The Challenger 604, for example, does use a third segment if the obstacle is below 1500' AGL. The aircraft is flown to obstacle height at V2 at which point it is accelerated, flaps are retracted, and climb is continued at VFTO. If the obstacle is above 1500' AGL, the second segment is extended to obstacle height but no higher than 15,000' MSL or five minutes at takeoff thrust.


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

Challenger 604 Airplane Flight Manual, Publication No. CH 604 AFM, Rev 56, Jan 14/05.

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

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

Gulfstream GV Aircraft Operating Manual, GAC-AC-GV-OPS-0002, Revision 30, May 13, 2008