British Airways Boeing 777 crash – FAA updates Trent guidance

BA 777-200ER.jpg

There’s a new FAA airworthiness directive out today stemming from the British Airways Boeing 777 crash on short finals to Heathrow last year, and now taking in additional evidence from a similar incident involving just one engine last November, plus a heap of research by Boeing and Rolls-Royce. Details below. The BA accident involved a Trent-powered aircraft and so did the secondincident, which affected an engine on a Delta Air Lines aircraft.

Full AD text here.

Delta incident details here.

BA incident interim report here.

Key passages in new AD as follows:

SUPPLEMENTARY INFORMATION:

Discussion

On September 5, 2008, we issued AD 2008-19-04, amendment 39-15671 (73 FR 52909,

September 12, 2008). That AD applies to certain Boeing Model 777-200 and -300 series airplanes.

That AD requires revising the airplane flight manual (AFM) to include in-flight procedures for pilots

to follow in certain cold weather conditions and requires fuel circulation procedures on the ground

when certain conditions exist. That AD resulted from a report of uncommanded reduction in thrust on

both engines because of reduced fuel flows. The actions specified in that AD are intended to prevent

ice from accumulating in the main tank fuel feed system, which, when released, could result in a

restriction in the engine fuel system. Such a restriction could result in failure to achieve a commanded

thrust, and consequent forced landing of the airplane.

Actions Since AD Was Issued

Since we issued AD 2008-19-04, we received a report of a single-engine rollback as a result of

ice blocking the fuel oil heat exchanger (FOHE) on a Model 777 airplane equipped with Rolls-Royce

Model RB211-TRENT 800 series engines. The data confirm that ice accumulates in the fuel feed

system and releases after a high thrust command, creating blockage at the FOHE and resulting in the

inability of the engine to achieve the commanded thrust. Examination of the data from the rollback

shows that the second of two maximum thrust step climbs was performed approximately 40 minutes

prior to the thrust rollback. Ice was released within the fuel system during the step climbs and formed

a restriction at the FOHE of the affected engine, as evidenced by an increase in engine oil

temperature. Further analysis of the data shows that ice accretes in the fuel system more rapidly and

at warmer fuel temperatures than previously indicated, and ice may build up gradually on the FOHE

before causing the engine to rollback. The data from this event, in combination with Boeing fuel lab

testing, demonstrates that reducing the fuel flow to minimum idle levels will clear any ice

accumulation at the FOHE within a few seconds.

All of the testing and research has been conducted on Boeing Model 777-200 and -300 series

airplanes, equipped with Rolls-Royce Model RB211-TRENT 800 series engines. Initial review of

other Model 777 airplane engine combinations has not revealed the same vulnerability to the

identified unsafe condition.

3

FAA’s Determination and Requirements of This AD

The unsafe condition described previously is likely to exist or develop on other airplanes of the

same type design. For this reason, we are issuing this AD to supersede AD 2008-19-04. This new AD

retains the fuel circulation procedures. This new AD also requires revising the AFM procedures

required by AD 2008-19-04. This AD revises the AFM in-flight procedures by reducing the step

climb from 3 to 2 hours prior to descent, and by requiring flightcrews to retard the throttles to

minimum idle for 30 seconds at the top of descent ensuring any ice accumulation on the face of the

FOHE melts while the airplane is at higher altitudes. Performing all step climbs using vertical

navigation (VNAV) or maximum climb thrust continues in this AD for all flights.

Paragraph (g) of AD 2008-19-04 requires that the fuel circulation procedures be accomplished

by a certified mechanic. We are retaining this requirement because of the complexity of the

procedure. We recognize that persons other than mechanics who are properly trained might also be

capable of accomplishing this procedure. Therefore, we would be receptive to requests for approval

of alternative methods of compliance in accordance with paragraph (k) of this AD to allow others to

accomplish the procedure if the request includes training and oversight provisions to ensure that the

procedure is accomplished properly.

Interim Action

We consider this AD interim action. The manufacturer is currently developing a modification

that will address the unsafe condition identified in this AD. Once this modification is developed,

approved, and available, we might consider additional rulemaking.

FAA’s Justification



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