4 Engine aircraft climb minimums

[lymanm]

Wannabe here...

Maybe some of you A340/747 (DC-8/707?) drivers out there can answer a nagging question of mine: what are the requiements of 4-engined aircraft in terms of engine failures at critical times during the flight? For example, if 1 or 2 engines are lost on take-off, what type of performance must be met by the remaining engines? Generally, can 1 engine maintain altitude? (I know there are many factors invlolved, so humour me)

Cheers

[quid]

MTOW is restricted to that weight which will allow no less than a 3% gradient in second segment if one engine fails on t/o. There is no requirement for losing two.

If you DO lose 2 just after t/o, you've got a fighting chance unless it's very hot and you're heavy. Then it's *overboost* power to try to save it.

If you're clean, and at landing weights, it will fly on one.

[Genghis the Engineer]

The legal requirement, in FAR/JAR-25 is that the aircraft must maintain a 1.5% climb, with the critical engine inoperative, at 5,000ft sHp / ISA.

The handling requirement in the same documents (which only apply to airliners) is that following engine failure and a 2 second delay before reaction, there must be no more than 20° heading change and the aircraft must be controlled within 5° of bank at MTOP.

Light twins below 19000lb don't have the performance requirement. All light twins have to be controllable within 45° maximum bank angle following an engine failure and 2 second delay at MCP.

G

[This message has been edited by Genghis the Engineer (edited 04 May 2001).]

[quid]

Guys-

Here is the applicable qoute from the FAR:

Sec. 25.121 Climb: One-engine-inoperative.
(a) Takeoff; landing gear extended. In the critical takeoff configuration existing along the flight path (between the points at which the airplane reaches VLOF and at which the landing gear is fully retracted) and in the configuration used in Sec. 25.111 but without ground effect, the steady gradient of climb must be positive for two-engine airplanes, and not less than 0.3 percent for three-engine airplanes or 0.5 percent for four-engine airplanes, at VLOF and with--
(1) The critical engine inoperative and the remaining engines at the power or thrust available when retraction of the landing gear is begun in accordance with Sec. 25.111 unless there is a more critical power operating condition existing later along the flight path but before the point at which the landing gear is fully retracted; and
(2) The weight equal to the weight existing when retraction of the landing gear is begun, determined under Sec. 25.111.
(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, 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 and with--
(1) 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
(2) The weight equal to the weight existing when the airplane's landing gear is fully retracted, determined under Sec. 25.111.
(c) Final takeoff. In the en route configuration at the end of the takeoff path determined in accordance with Sec. 25.111, the steady gradient of climb may not be less than 1.2 percent for two-engine airplanes, 1.5 percent for three-engine airplanes, and 1.7 percent for four-engine airplanes, at not less than 1.25 VS and with--
(1) The critical engine inoperative and the remaining engines at the available maximum continuous power or thrust; and
(2) The weight equal to the weight existing at the end of the takeoff path, determined under Sec. 25.111.

Now, once under way and the a/c is in the clean configuration, the following applies:

Sec. 25.123 En route flight paths.
(a) For the en route configuration, the flight paths prescribed in paragraphs (b) and (c) of this section must be determined at each weight, altitude, and ambient temperature, within the operating limits established for the airplane. The variation of weight along the flight path, accounting for the progressive consumption of fuel and oil by the operating engines, may be included in the computation. The flight paths must be determined at any selected speed, with--
(1) The most unfavorable center of gravity;
(2) The critical engines inoperative;
(3) The remaining engines at the available maximum continuous power or thrust; and
(4) The means for controlling the engine-cooling air supply in the position that provides adequate cooling in the hot-day condition.
(b) The one-engine-inoperative net flight path data must represent the actual climb performance diminished by a gradient of climb of 1.1 percent for two-engine airplanes, 1.4 percent for three-engine airplanes, and 1.6 percent for four-engine airplanes.
(c) For three- or four-engine airplanes, the two-engine-inoperative net flight path data must represent the actual climb performance diminished by a gradient of climb of 0.3 percent for three-engine airplanes and 0.5 percent for four-engine airplanes.

So, for the *takeoff*, no consideration is made for the failure of a second engine.

[This message has been edited by quid (edited 04 May 2001).]

[This message has been edited by quid (edited 04 May 2001).]

[fly4fud]

and all of this, of course, also applies to the ARJ (and BA46) as well :)

(yes, we call'em engines, not vacum cleaners or APUs :) )

------------------
... cut my wings and I'll die ...

[john_tullamarine]

Also, chaps, do keep in mind that ..

(a) the design and operating standards are living and evolving beasts ..they keep changing .. therefore

(b) it is not correct to look at a particular version of a standard unless you first check the TCDS for the frozen standard applicable to the type and model..and then find a copy of the standard at that A/L version... and, even then, the manufacturer negotiates concession deals with the design authority and these are not usually public domain ...

(c) disregarding the different performance numbers for different number of motors .. the basic FAR 25 deal is ... the aircraft has to be able to lose a motor at any stage of flight and have a predictable means of successfully terminating the flight. In addition, if the aircraft is not able to maintain appropriate performance with a second motor out, then it is subject to the normal two engine distance limitations ...

(d) thoughts of continued T/O in a light twin, unless at well below MTOW and on a cold day ... are frought with hazard ... both from handling and terrain clearance points of view ...

[Zeke]

Genghis the Engineer,

Twins over 12,500 pounds (5700 kg) certified FAR 23/CAR 3, SFAR 41 or FAR 25 do have performance requirements as per FAR 23/CAR 3, SFAR 41 or FAR 25 .

FAR 23/CAR 3 aircraft do have a first segment climb gradient of postive at V1 (V1 >= 1.1 Vs 1.1 Vmc), second segement >= 2% at V2 up to 400 ft, third segment gradient of 1.2% at 1500 ft, require to have 50 ft screen on the runway to calculate takeoff distance, approach climb OIE >= 2.1% @ Vref, landing climb gradient of 3.3%.

Some jets below 12,500 lb elect to have performace requirements set as per FAR 25.

john_tullamarine,

I agree that the TCDS need to be consulted to determine the certification basis. However the certification requirements (FAR 23 / CAR 3 / SFAR 41C / SFAR 41C ANNEX 8 / FAR 25), are only half the picture you must also look at the operational requirements set out by the local ICAO contracting state, and the ICAO contracting state that the aircraft is registered in as to their particular operational requirements to determine obstacle clearance and runway requirements. Local operational requirements may stipulate for example that the manufacturers data for takeoff distance must be multiplied by a factor of 1.15, and landing by 1.67.

:rolleyes:

[Genghis the Engineer]

Thanks for pointing out my error - 12,500 lb / 5,700 kg it is, not 19,500 lb, which is the 23 / 25 threshold. But the biggie is John's point that the frozen certification standard quoted in the TCDS is the bottom line. There are aircraft out there certified against Section D, Section K, and all sorts of other archaic standards.

I doubt however that many light twins will "elect" to comply with JAR/FAR-25. They may well actually comply, but no Chief Engineer is going to certify to a higher standard than he absolutely has to - the initial costs and potential long term inconvenience are not worth the hassle in exchange for the slight warm glow of having an aircraft certified to a slightly higher standard.

G