View Full Version : Uncommanded Dive of 737

mary meagher
15th Apr 2009, 13:24
Boeing 737, 12 Jan. 2009, West of Norwich.

Has this incident been covered anywhere? I am too intimidated to ask the question on the Rumors and News or the Questions, which is off limits for this timid old lady, who doesn't get any money for flying aeroplanes......

Looks like due to a communication problem, during supplementary maintenance, balance tabs were adjusted the wrong way, and on the subsequent check ride when the hydraulics were turned off, the out of trim situation resulted in a dive. And the handbooks (Boeing vs. CAA) seemed to differ in their suggestions as to what to do next.

I would like to read all the comments, can you tell me where to find them?

Curious Pax
15th Apr 2009, 13:27
Yep - take a look at Easyjet pitch down incident (http://www.pprune.org/rumours-news/358016-easyjet-b737-pitch-down-incident-12-january.html)

15th Apr 2009, 13:27
If true, then all this does is prove the worth of a test flight before return to service.

Probably a non event, hence the lack of reporting (if it did happen)

15th Apr 2009, 14:13
Very much NOT a non-event ! but a good illustration of how much automated systems can disguise an out-of-trim condition, and what happens when that system is suddenly disabled, either through a failure or during testing.

There are numerous incidences of an aircraft under test flying in a completely stable condition but when electric or hydraulic systems are disabled, massive amounts of trim have to be wound on very quickly as aerodynamic forces act on control surfaces freed of automatic trim.

In some cases the flying officer is advised to remove his hands from the controls before pulling off electrics or hydraulics as they can move rapidly and very forcefully during what is called manual reversion.

And yes, an uncommanded dive (or many other things) may happen during a test flight or when a failure occurs.

15th Apr 2009, 16:02
Do test pilots get a special tax free laundry allowance? That report suggests they could well need it.

15th Apr 2009, 16:35
.. thought there was viagra for this specific problem ..

15th Apr 2009, 16:44
Mary, are you the timid old lady and do you fly and is that why you're asking ?

Understand your trepidation if the answers are yes, but as always when travelling by ANY transportation the word is "keep a sense of perspective".

Frequently when hurtling down the runway at 200 kph (or whatever) I look out of the window and think "what if...." but it all comes down to the chances of something happening and statistically they are very very small, as small as small can be.

And if they do, at least in Europe* and the US*, you've got extremely well-trained crew to deal with such things.

My own receipe for dispelling such thoughts is two stiff pastis/Ricards before departure, and a good book.....

* My apologies to everywhere else. I speak from prejudice and ignorance (but don't we all ?)


15th Apr 2009, 18:40
From the April AAIB Bulletins;

During the ferry flight to deliver the aircraft to the maintenance provider, the operator had flown a ‘shakedown’ test using the same customer ‘demonstration flight test schedule’ to identify any existing defects, allowing rectification work to be completed during the maintenance input. This ‘shakedown’ flight included the manual reversion test to assess the trim of the aircraft. This involved switching off both hydraulic systems powering the aircraft flight controls and assessing the amount of manual stabiliser trim wheel adjustment required to balance the aircraft in level flight. The results of this test identified that the aircraft was within, but very close to, the approved maintenance manual limits. Following the flight, the commander verbally requested that this be addressed during the subsequent maintenance input, but elected not to enter it in the tech log, as the level of stabiliser trim required during the test had been within limits. The absence of a formal post‑flight debrief and formal written record resulted in the balance tabs, attached to the elevators of the aircraft, being adjusted in the opposite sense to that identified as necessary by the flight test. The aircraft was therefore significantly out of trim during the post-maintenance test flight, and it was that which initiated the pitch-down incident during the manual reversion test.

15th Apr 2009, 19:47
I wish!:ok:

15th Apr 2009, 22:17

Incident reported in this months AAIB report.

Started at FL150. A/c banked over the vertical. initial unstoppable descent at c.3,000fpm.

ROD increased to a max value of 21,000 fpm.

It certainly would have got my attention!;)

Mary. The AAIB sent me their digest every month. It's FOC.
Alternatively I believe you'll find it online. AAIB.gov or similar

15th Apr 2009, 22:59
I had an uncommanded dive in a 727 once.

Tripped coming down the aft airstair once. :uhoh:

(The prisoners thought it was funny. :()

(Hey, this is in JB after all. ;))

mary meagher
16th Apr 2009, 11:59
OFSO, thank you for your kind words. I am an old lady (old woman) to be sure, & started flying gliders at the age of 50 in 1983, so you can work that one out. I am timid because in the August Company of all these Professional Pilot Prunes, I don't want to ask stupid questions; didn't join until after Capt.Sully, with his gliding background, made such a splendid approach on the only runway available at the moment.

Back in 1983, there were not many girls in the cockpit, (with their hands on the controls) so realistically was unlikely to qualify to fly Boeings. Nevertheless have accumulated 3,000 hours in this and that. Still basically chicken, however.

Barbie's Boyfriend, thank you for the tip; that's where I found the item, and wondered what would be on PPrune about it. Fortunately I have an engineer who actually flies my PA18 after maintenance. . . .

16th Apr 2009, 17:01
I was seeing the wife off to London this afternoon at GRN. It was storming and hailing and raining and slush-snowing, bits and pieces of ice banging off the roof of my car - I was shelting in the car under a tree and there were another half dozen other cowardly drivers sitting the storm out. Unlike the Transavia and FR 737's of course which were blithly coming and going with no trouble.

It's all relative. (Sure was noisy though).