Learjet flutter

[DH1]

Some years ago a number of Learjets broke up mysteriously in mid flight. After much investigation, the cause was found to be blocked drains in the wings. On a rainy day water would accumulate in the wing that would freeze near the training edge during climb.

Aparently this then made the Learjet susceptable to catostrophic flutter.

Question is:

1. How did the ice cause flutter?

2. How did they ever figure this out since the ice would have melted by the time the investigators arrived on scene?

Any ideas?

[con-pilot]

Actually it was the elevators that had the icing problems. The wing problem was during over MMO limit the ailerons would start fluttering and remove itself and the wing, which would tend to put an instant end to the flight.

Another problem was that when the wing spoilers were deployed it caused a nose tucking action and the airplane would actually accelerate causing more problems. The fix was to train that in an over MMO emergency situation to lower the landing gear, the gear doors would depart the airframe, but the wings wouldn’t.

This on the early 23/24/25 series Lears, starting with the 30 series the spoilers were relocated and were tied into the ailerons and the problem was solved.

[palgia]

1. Water freezing as ice adds weight and unbalances the control surfaces, making them more prone to flutter. The US Navy had similar problems when they put too many layers of paint on top of the other thus adding weight and unbalancing some control surfaces.

2. That would not be too hard. First of all how do we know it was not freezing at the surface? How fast were the investigators there? The recording of ice and/or other perishable evidence are among the initial actions investigators do when arriving at an accident site. Either way, evidence of control flutter is very easy to spot, and there are not many ways the control can get unbalanced. If you add on top of that the fact that maybe some drain holes were found clogged, that it was rainy at the departure airport and control unbalance due to icing is a known problem, it wasn't too hard to figure out the cause of the flutter.
Evidence of control flutter is common at many accident sites. However that is mostly due to overspeed. In this case they might have calculated that the speed at which the flutter occurred was not beyond the aircraft's envelope.
If you read the accident reports for the flight in question I'm sure you will find more explanations.

palgia