Ice Bridging-Myth or Reality?

[Victor Meldrew]

A big factor in shedding the ice is boot condition. Dirty or rough boots will allow the ice to adhere better (like roughing down a surface before you paint it). Properly treated and protected boots will allow the ice to shed when the boots blow.

Another factor is speed. Airflow also helps force the broken ice off the surfaces. The only booted a/c I flew regulary in ice was the C208B, let it's speed drop to below 120 KIAS with ice and then blow the boots you'd see most of it stay and you were then prime for bridging.

 

[Tim47SIP]

Icing tests!

I don't think Roselawn had anything to do with Ice Bridging.


OK, I should have been more specific. The bridging occurred during the icing tests done at Edwards AFB after the accident. If you remember, the French blamed the accident on the crews failure to get out of icing, the delay in using the de icing system, and holding with flaps 15. The NTSB didn't buy the explanations and decided to try and determine the amount of icing that adhered to the aircraft. What they found was that icing formed past the effective range of the boots and as the ice built up it moved forward. This formation was well outside the effective range of the forward part of the boots. The NTSB believes that the tail stalled and then the violent roll due to the angle of decent. Ice bridging may not have formed on the Roselawn aircraft but it did form on the right wing (test wing) of the Edwards aircraft. These tests are what spurred the re engineering of the de icing system as well as the new procedures put into place after the accident. ATR was livid and insisted that the aircraft met the FAA's requirements for icing. The aircraft had never been certified in heavy icing. There were several ATR's that crashed in heavy icing prior to the Roselawn crash which moved the NTSB towards the icing tests at Edwards. You can look up the reports on the NTSB site which also has the petitions from the French government to change the cause of the the accident from what the NTSB determined. There are also some very good icing pictures on their site.

 

[mckpickle]

I don't think Roselawn had anything to do with Ice Bridging.


OK, I should have been more specific. The bridging occurred during the icing tests done at Edwards AFB after the accident. If you remember, the French blamed the accident on the crews failure to get out of icing, the delay in using the de icing system, and holding with flaps 15. The NTSB didn't buy the explanations and decided to try and determine the amount of icing that adhered to the aircraft. What they found was that icing formed past the effective range of the boots and as the ice built up it moved forward. This formation was well outside the effective range of the forward part of the boots. The NTSB believes that the tail stalled and then the violent roll due to the angle of decent. Ice bridging may not have formed on the Roselawn aircraft but it did form on the right wing (test wing) of the Edwards aircraft. These tests are what spurred the re engineering of the de icing system as well as the new procedures put into place after the accident. ATR was livid and insisted that the aircraft met the FAA's requirements for icing. The aircraft had never been certified in heavy icing. There were several ATR's that crashed in heavy icing prior to the Roselawn crash which moved the NTSB towards the icing tests at Edwards. You can look up the reports on the NTSB site which also has the petitions from the French government to change the cause of the the accident from what the NTSB determined. There are also some very good icing pictures on their site.

What other ATR crashed due to Icing? Also, the tail did not stall due to the ice. When the pilots retracted the flaps the A/C flipped over. The ailerons had effectively stalled out due to the blocking of airflow in front of the outboard wind section. When the flaps came up the autopilot could no longer hold the a/c because the ailerons where "fluttering". To my knowlege the only other ATR incident occured when one experienced a uncommanded roll on arrival in EWR. The crew held onto the a/c and landed. The incident in Roselawn did have issues with the SCDD (super cooled drizzle droplets), and the tests proved that no a/c with boots could have survived. You have to question the crew holding in those conditions for that amount of time.