Jan 16, 2008

Turbulence a less likely culprit...

Comments found online regarding the recent Air Canada A319 "upset" incident now seem to reduce the likelihood that turbulence was the culprit.

For example, this comment by a jet transport pilot who was a passenger on AC190 (emphasis added):

http://www.avcanada.caforum....
...
I was on AC 190 yesterday. ... we were in smooth air in cruise when the plane rolled abruptly to the left followed by a roll reversal to the right. There were then about 3 more roll reversal that were getting small in intensity. It seemed to me that after the first roll upset the crew was getting the Plane back under control. ... After the crew had the Plane back under control the Captain made a PA and said that they had had a computer malfunction and that the problem had been isolated and that they were manually flying the Plane. The rest of the flight was smooth with a nice landing in YYC. I just wanted to say thank you to the crew for getting us on the ground safely.

Then, these comments from a Transport Safety Board official as quoted by CBC (again, emphasis mine):

http://www.cbc.ca/canada/story/2008/...t-calgary.html
...
"The aircraft rolled to the right to about 35 degrees of bank and rolled to the left about 50 degrees of bank and effectively the auto pilot was disconnected," said Nick Stoss of the Transportation Safety Board.


The upset was apparently a sudden rolling movement of the aircraft which is not what I would expect from CAT/Turbulence encounters. Further laying the CAT hypothesis to rest are the comments about smooth air before and after the incident, and a previous report that said that the pilots did not log an official report of turbulence with ATC.

Flight control problems of one sort and another now take on greater importance in my mind. A sudden roll to one side (interestingly the two reports differ about which direction happened first.) followed by an even further roll in the opposite direction followed by diminishing rolls suggests that one or both pilots over-reacted to the sudden movement, causing momentary oscillations, before restabilizing the plane to level flight.

Reports of the aircraft "plunging" are also easily explained. Any time an aircraft banks to extreme angles it becomes more difficult to maintain altitude. This is exaggerated the higher we climb into the thinning atmosphere. So along with any altitude loss caused by those huge rolling movements, I'm sure the pilot also initiated an immediate descent.

What sort of malfunctions might be suspected? More thoughts on that coming up...

3 comments:

Teller said...

Perhaps the discrepancy in the direction of the initial roll is easily explained? If the first roll was only 35 degrees to the right, maybe it either wasn't felt or seemed normal to a passenger in the back, then the 50 degree roll to the left would have been the first upset a passenger without an ADI would have noticed. Just a thought. Sounds like an event I wouldn't care much to experience!

Anonymous said...

Reading articles about ACA190 with interest as my wife and I were passengers this flight. We were in the back and most definitely felt the initial roll to the left then right. Never experienced 'turbulance' like that before. Have heard of rumours of another aircraft near-by but no one has identified it. Interesting that no one has mentioned that the personal entertainment system was non-functional when we departed YYJ - we are still waiting for the promised voucher for not having entertainment. Sure glad we keep our seat belts on!

Aluwings said...

Anonymous - How much more entertainment do you need than an unexpected roller coaster ride at 30,000+ feet! lol

Seriously, I'm glad you and your wife were not injured and "good for you" regarding the seatbelt. That's my practice too when riding as a passenger.

I just posted another item regarding the possibility of wake turbulence and wing tip vortices being the cause. Thanks for posting your comments.

p.s. I hope you get those vouchers soon and that they are not free passes to the local amusement park!