Engine failure on Trijets
 

Hi there,

I just had a debate with my colleague if Trijets such as a Falcon 7X or a MD11 is subject to Single Engine climb gradients if only one engine fails during takeoff? Obviously the loss of one engine with two remaining operarational isn't 50% thrust loss. How is that calculated and how is the performance of a 3 holer jet affected when it comes to obstable clearence? Maybe a too general question because of numerous factors but I am curious to hear what you experts say...

Cheers

Hi Proline,

About the MD-11... Yes, it's affected and in some scenarios pilots must follow an engine-out climb procedure in order to comply with the obstacle clearance criteria.

How is it calculated? For reference, there are some tables in the Performance Manual.

I would say "yes". Since the logical failure is a single engine, it must have sufficient thrust at that point to achieve the single engine climb gradient. With all three engines running it has 50% additional power, compared to the extra 100% on a twin-jet and the 33% on a four-engine.

All perf A aircraft (with 2,3 or 4 engines) have to plan on having one engine fail on take off.
In the case of the TriStar (L1011) on take off from LGW 26L, we had to "swing the cone" (15 degrees left turn with 15 degrees bank - to avoid Russ Hill) with an engine failure.

If we were light, we could do a single engine GA (with 2 engines failed) from about 1500 feet on the approach by descending on the glide path whist accelerating to enable a clean wing then "climb" away (more of a limp really).

Same on B727.

Second segment climb
 

Three engined jets have higher required second climb gradient. So the performance of two vs three engined jets can not be directly compared.

Single engine climb gradient
 

NO .. only one engine out climb gradient taken into consideration.
Infamous incident on a Trident 3 airborne from Malaga iirc and lost an engine shortly afterwards. Crew didn't check the WAT performance before they diverted to Madrid, typical useless atc for that time lined up an Iberia which forced a missed approach. Aircraft continued descending; skipper fortunately cleaned up to min drag (230 knots?) and accelerated down the valleys which gave him enough performance to return to land.

Thanks guys for the insight! cheers!

From 14 CFR 25.121:

(b) Takeoff; landing gear retracted. In the takeoff configuration existing at the point of the flight path at which the landing gear is fully retracted, and in the configuration used in Sec. 25.111 but without ground effect:

• (1) The steady gradient of climb may not be less than 2.4 percent for two-engine airplanes, 2.7 percent for three-engine airplanes, and 3.0 percent for four-engine airplanes, at V2 with:
  • (i) The critical engine inoperative, the remaining engines at the takeoff power or thrust available at the time the landing gear is fully retracted, determined under Sec. 25.111, unless there is a more critical power operating condition existing later along the flight path but before the point where the airplane reaches a height of 400 feet above the takeoff surface; and(ii) The weight equal to the weight existing when the airplane's landing gear is fully retracted, determined under Sec. 25.111.