Captain John Marriott
BALPA Safety Rep
You’re belting down the runway at great speed when a door warning message pops up. Would you call ‘Stop!’? As an accident investigator, a number of similar events have crossed our desk, provoking some interesting discussions around the table.

I think it’s one of those things worthy of prior evaluation or discussion because of the fact that you would have little time for analysis at 120 knots and rising. You might simultaneously get a takeoff configuration warning going off that could be very compelling, and most operations manuals would automatically require a call or stop, reject, or whatever your company call is.

On many aircraft types, the takeoff configuration warning for certain things is inhibited at high speed, so you might only get the message or caption. The first useful bit of information to know on your aircraft type is which doors are plug fit and which aren’t. I think it’s safe to say that, generally, in the majority of modern airliners, most cabin doors are plug fit and most hold doors aren’t.

There are, of course, exceptions. For example, the bulk door on my B777 ER is a plug fit and the rear door in the B777 – 200 (commonly known as the A Market aircraft) is like a cabin door, in that it opens outwards but is cleverly a plug fit. Anyway, my personal thoughts are these: if I’m happy that the door message is a plug fit door, I’m also happy it’s not going anywhere and therefore presents little risk to the operation.

Think twice

If the high-speed door message is, for example, a hold door that I know opens outwards, I’d think twice – but not for long of course, as V1 is approaching rapidly! I’d certainly consider calling stop/reject in this case, especially if accompanied by a pressure change, vibration or noise, as I can envisage the airflow at rotation getting behind an unsecure hold door, ripping it off, and subsequently colliding with the tail plane. Now, I’ve lost a tail plane in flight before, but that’s another story; I certainly don’t want to experience it again.

Another consideration is that on many types of aircraft the outflow valves close while the aircraft accelerates along the runway, thereby pressuring the fuselage. A plug fit door would simply be pushed further into its hole, but an outward-opening door – if not properly secured – could be forced open.

How about making a mental assessment of the acceleration/stop margin before the departure? This way there would be less of a problem stopping up to V1 if there was plenty of distance in hand; close to V1 on a limiting length runway might be a different matter, of course. If you are doing a packs-off takeoff for performance reasons, combined with a roughly surfaced runway, maybe a plug fit door warning of some sort would be more likely? And what if ATC called for you to stop at high speed? Would you call stop?
This article first appeared in The Log Autumn 2016
Comments 1
Comments
Martin Alder
During a packs off ,.ie unpressurised take - off a plug door that effectively relies on gravity to stay closed is not quite so certainly closed as it would be if the designed pre-pressurisation via a packs on take - off were used. This design configuration also locks the door more firmly in place and reduces, if not eliminates the nuisance unlocked warnings of the sort that gave one UK carrier some 60 or do RTO s in a 12 to 18 month period, possibly triggered by rougher runways at some airports.
Note that some cargo doors even though outward opening will not open if pressurised due to the design of the over center latches being such as to not be openable when pressurised.
What about an over wing hatch being opened by a passenger and deploying a slide? Not possible if pressurised but could be if unpressurised?
So all in all, ignoring a door warning even for plug doors would have a risk if taking off unpressurised. So, not quite so easy to ignore as it might first appear. It is yet another reason to stick with the intended design techniques for operating the aircraft. After all, more de -rate or flex has as a consequence a higher fuel burn due to a longer take off roll and lower acceleration and climb rates that may for some types easily outweigh any notional economic gains due to lower EGT . This is especially true at larger derate values.
20/10/2016 23:02:44