Transpac787
Topic Author
Posts: 1349
Joined: Mon Jul 30, 2007 12:47 pm

Fuel X-Feed Requirements On Etops

Thu Dec 20, 2007 2:56 am

Hey all,

Simple question.....what is the fuel crossfeed requirement for a twin on ETOPS?? I've heard two sides to this:

A) Two crossfeeds are required, if a twin is to fly ETOPS
B) Only one is required, so long as it is tested on the ground and in the air prior to feet-wet

The only reason I was wondering is, I've seen AA's 762ER's fly ETOPS routes to Hawaii and LHR among other places, and they only have a single crossfeed. Also, this past fall I flew AA63 CDG-MIA, and that specific aircraft (N368AA), only had a single x-feed valve.

Anyhow, anyone who can shed light on this issue I'd much appreciate.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Fuel X-Feed Requirements On Etops

Thu Dec 20, 2007 3:53 am



Quoting Transpac787 (Thread starter):
Simple question.....what is the fuel crossfeed requirement for a twin on ETOPS?? I've heard two sides to this:

A) Two crossfeeds are required, if a twin is to fly ETOPS
B) Only one is required, so long as it is tested on the ground and in the air prior to feet-wet

Yes.

It depends on the model and the ETOPS rating. No 737 was ever built with a dual crossfeed but they can be ETOPS certified. 757 and 767 come in both versions (single and dual crossfeed). 777 is only available with dual crossfeed.

It's not a strict requirement on the design, it's a requirement that the aircraft be able to reach the diversion airport with one engine. When you go through the whole systems analysis process that will drive you down to what failure rate you can tolerate for the crossfeed valve (function of fuel capacities, specific design features, ETOPS rating, etc.).

Tom.
 
dl757md
Posts: 1483
Joined: Mon May 24, 2004 9:32 am

RE: Fuel X-Feed Requirements On Etops

Thu Dec 20, 2007 4:32 am

Per the FARs quoted below (relevant sections in bold) it is not required to have 2 X-feeds unless you are exceeding 180 mins ETOPS and engine operation is adversely affected by negative fuel pump inlet pressure. In other words it won't gravity or suction feed from the tanks at all engine thrust settings and airplane attitudes.


K25.1.3 Airplane systems.

(a) Operation in icing conditions.

(1) The airplane must be certificated for operation in icing conditions in accordance with §25.1419.

(2) The airplane must be able to safely conduct an ETOPS diversion with the most critical ice accretion resulting from:

(i) Icing conditions encountered at an altitude that the airplane would have to fly following an engine failure or cabin decompression.

(ii) A 15-minute hold in the continuous maximum icing conditions specified in Appendix C of this part with a liquid water content factor of 1.0.

(iii) Ice accumulated during approach and landing in the icing conditions specified in Appendix C of this part.

(b) Electrical power supply. The airplane must be equipped with at least three independent sources of electrical power.

(c) Time limited systems. The applicant must define the system time capability of each ETOPS significant system that is time-limited.

K25.1.4 Propulsion systems.

(a) Fuel system design. Fuel necessary to complete an ETOPS flight (including a diversion for the longest time for which the applicant seeks approval) must be available to the operating engines at the pressure and fuel-flow required by §25.955 under any airplane failure condition not shown to be extremely improbable. Types of failures that must be considered include, but are not limited to: crossfeed valve failures, automatic fuel management system failures, and normal electrical power generation failures.

(1) If the engine has been certified for limited operation with negative engine-fuel-pump-inlet pressures, the following requirements apply:

(i) Airplane demonstration-testing must cover worst case cruise and diversion conditions involving:

(A) Fuel grade and temperature.

(B) Thrust or power variations.

(C) Turbulence and negative G.

(D) Fuel system components degraded within their approved maintenance limits.

(ii) Unusable-fuel quantity in the suction feed configuration must be determined in accordance with §25.959.

(2) For two-engine airplanes to be certificated for ETOPS beyond 180 minutes, one fuel boost pump in each main tank and at least one crossfeed valve, or other means for transferring fuel, must be powered by an independent electrical power source other than the three power sources required to comply with section K25.1.3(b) of this appendix. This requirement does not apply if the normal fuel boost pressure, crossfeed valve actuation, or fuel transfer capability is not provided by electrical power.
757 Most beautiful airliner in the sky!
 
User avatar
jetmech
Posts: 2317
Joined: Wed Mar 29, 2006 2:14 am

RE: Fuel X-Feed Requirements On Etops

Thu Dec 20, 2007 5:17 am



Quoting Transpac787 (Thread starter):
Only one is required, so long as it is tested on the ground and in the air prior to feet-wet

IIRC, the A330 only has one cross-feed as well. With my current employer, the cross-feed is tested before every flight as part of the ETOPS check.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .

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