Boeing to modify 737s after near stall

On 26 December 2012, a Norwegian 737 on approach to Kittila almost stalled on final approach. The aircraft was under autothrottle/autopilot control when it began to nose up. The autothrottle commanded more power, which led to higher pitch. The crew pushed forward as they reached 20 degrees nose up, and were able to recover although the aircraft fought.

It was determined by investigators that deicing fluid can enter the tail cone of the aircraft, and contaminate the flight control cables. The fluid freezes on the PCU arms, restricting their ability to travel.

Boeing plans to release a modification to the deicing procedure, as well as to the aircraft itself to prevent fluid entry into the tail cone area, but hasn't specified what exactly.

Boeing is to modify 737s to improve protection against potential freezing of elevator systems, after investigation into a near-stall by a Norwegian aircraft highlighted the risk of de-icing fluid contaminating power control units for the horizontal stabiliser.

The investigation into the 737-800 incident, on approach to Kittila in Finland, has already resulted in Boeing changing de-icing procedures on the type. Under the new procedures the trim is set to take-off position, rather than fully-forward, and de-icing fluid is applied at an angle, not directly from the side.

While the cause of the incident is still being explored, Norwegian investigation authority SHT demonstrated that de-icing fluid was capable of entering the tail cone in “quite considerable” amounts.

“Under certain circumstances it is possible that the input arms [to the power control units] may be exposed to fluid which in turn freezes solid and blocks [them],” says SHT, adding that Boeing was “not aware” of this potential problem before the investigation.

www.flightglobal.com...

It seems that Boeing is having a few problems with their jets lately. They had such a good record with their earlier jets till they decided to create new super jets. They are caught up in a stupid belief that they need new and bigger aircraft so they could stay at the top of technology.

reply to post by rickymouse


The 737 is an older design. It's the most popular commercial aircraft built, and has something like 9,000 examples built and on order. They first noticed this problem with an older model of it.

Makes me wonder about the Kazan crash a few weeks ago.

reply to post by JIMC5499


That one so far is coming across pretty cut and dried, but yeah, it does open up a few questions with that one.

De-Icing fluid....freezing (!) the controls of the aircraft.

Hilarious. Somehow.

reply to post by NoRulesAllowed


Yeah, I know. I noticed the irony of that myself when I read the article.

reply to post by Zaphod58


What was the preliminary thought on what caused that one?

reply to post by Sammamishman


Crew error. The nose pitched up to 25 degrees, and they thought they were going to stall so they pushed forward on the stick, and dropped the nose down to 70 degrees nose low.

reply to post by Zaphod58


Is this related at all to the 747 and 787 GenX icing issues with the current no fly within 50 kilometers of electrical storms?

reply to post by Zaphod58


Well since the OP is about my current airline, the modifications includes all B737-800's (NG's) 2006 and on.
The fix seems to be drain tubes in the tail section.

Is this related at all to the 747 and 787 GenX icing issues with the current no fly within 50 kilometers of electrical storms?

No, that's about engine icing.

Have a look at this thread: www.pprune.org...

reply to post by Ivar_Karlsen



Didn't see that:

Under the new procedures the trim is set to take-off position, rather than fully-forward

Yup, sort of, 5 units of stab trim is to be set for de icing.

reply to post by Ivar_Karlsen


You're a doll. Great read. The prune thing.

reply to post by luxordelphi


The two aren't related in any way. One has to do with engines, one has to do with deicing fluid getting into areas it's not supposed to.