The Door With No Name

Air Safety Week, March 26, 2007

A Case Of Unachievable Access

When an aircraft enters heavy maintenance and something is removed, it's normal procedure for a job card to be raised to ensure that it is eventually replaced. That's been the law of the hangar jungle for decades now.

But what if that item, although safety critical, doesn't rate a mention in the applicable section of the aircraft's maintenance manual (AMM)? Will that item have a job card raised? If not, how (and who) among the three shifts working that project will ensure that it's refitted?

That's a question that the United Kingdom Air Accident Board investigators of a June 10, 2004 Heathrow Boeing 777 incident started asking.

It's also the sort of safety-related issue that will be closely examined by an April 11 webinar, entitled: Aviation Maintenance: Trends That Will Affect Your Bottom Line in 2007 (for more details or to register, go to www.AviationToday.com).

As this forthcoming webinar will explain, it's not uncommon for items to be "left off", or even "left behind" after heavy maintenance.

For example, in a Jan. 6 incident, a QANTAS 747-400 made it from its heavy maintenance session at Avalon Victoria to Sydney NSW, picked up a load of passengers and then, as QF5, was most of the way to Singapore (Frankfurt next) when a bit of it was discovered to be still at Avalon. (See Air Safety Week, Feb. 5 issue, "The Yellow Logic of Chicken Little".)

A large panel had been found atop a maintenance docking stand. VH-OJA diverted into Jakarta where a new panel was fabricated, a necessary step because the panel was structural (i.e., load-carrying). That took six hours. Why wasn't it picked up by engineers or pilots on a walk-round? Because other panels must be removed to even see it, let alone get at it. The case for job-cards is well- proven.

On June 10, when the British Airways 777-200ER got airborne for Harare, Zimbabwe, it was leaving a heavy tell-tale trail of fuel vapor streaming behind it. Luckily that was noticed by another aircraft and the BA crew was informed. They dumped fuel and landed G-YMME rather cautiously, doing all they could to avoid hot brakes by using the lowest autobrake setting.

This time, the panel that had been left off was a center wing fuel-tank (CWT) purge door located up inside the left main landing gear bay. Not only was it a door that should've been replaced, it also qualified, as an integral part of the fuel-tank, to be leak-checked. When that leak-check was carried out, with no record of the purge door's removal, the visual inspection for leaks didn't include the purge door's location.

The fuel level erroneously specified in the AMM was for a 747 and below the level of the 777's purge door, so nothing could've been disclosed anyway. Few among those working on the aircraft during its heavy maintenance at Cardiff Wales were even aware of the existence of the purge door. But what had happened to it? How come it had not been noticed laying around?

As it turned out, it was found in the airplane, hanging on its lanyard inside the fuel-tank. A plastic bag containing its securing bolts was attached to the purge door's outer opening, with the door's sealing O-ring (see tinyurl.com/2yd2tl). When the inboard main gear door is closed, as it normally is on the ground, the purge door is not visible from ground-level.

The procedure in the AMM for emptying and vapor purging the tank to permit human entry made no mention of a purge door. Completely stand-alone and elsewhere in the AMM (and not cross-referenced to the fume removal procedure) was a purge door Removal/Installation procedure.

This rigmarole was different to the 747 procedure in that the 747's purge door could have its bolts removed, fall into the center tank and later be pulled back into position by its lanyard for securing. The suspicion must be that the process was mindlessly begun per the 747 procedure, by one individual, and not picked up by the next shift. BAMC, the Cardiff-based maint organization for BA, maintains both 747 and 777 aircraft.

Nevertheless, if the fuel amount for the center section tank leak check had been sufficient to reach the gaping hole, the missing door would have been located at Cardiff (as fuel poured out). The leak check fuel amount has now been increased from 32,000kg to 52,163 kg in order to meet that fuel level requirement.

Amazingly, the aircraft then flew 53 sectors between the completion of its heavy maintenance on May 10 and the incident date of June 10. On those flights, the highest fuel level carried in the CWT had been 26,800kgs, half the amount required to immerse the opening.

Because job cards are computer initiated by the stepped processes set out in the AMM, no job card had ever been raised to remove the purge door or later replace or leak-check it. It was evidently a case of someone getting ahead of the game and dangerously using his initiative, then going off shift. No-one would admit to having removed the door.

The AAIB went over the records of previous 777 checks at BAMC Cardiff and discovered instances of job cards having been raised to refit the purge door, but none to remove it. In no case had sufficient fuel been loaded to leak-check the purge door. In the prior case of G-YMMA, the missing door had been noticed by an experienced engineer but he had only raised a defect card to have it replaced and did not take that maintenance error any further.