Although i have no practical experience (thank god!) when read some of those ice related accident reports i have the feeling that in severe (or even moderate) icing conditions things can happen very very quickly… That TBM story, but Colgan Air and Roselawn (ATR) too are very scary stories… and i plan to never make any practical tests …
Peter, that is what I am getting at. Even in the TBM video, the icing takes some time to occur. It isn’t instantaneous. Or if it is you have other problems.
I think that TBM encountered really exceptionally severe icing – this is supported by the reports from jet pilots collecting several inches of ice in that area.
It was all over for him, from maybe the first moment ice was noticed, to being out of control, in a few minutes.
What can one do about it?
Probably nothing – apart from not flying in that sort of weather in the first place. But if you paid $3.xM for a TBM, are you going to avoid frontal weather for example? If you do, your despatch rate will be that of a TB21 with no TKS. I am sure that people that fly these types will despatch into any weather (short of zero-zero fog, or a TS right above the runway) and use the radar to avoid the cells. That is basically what airliners do.
Anyway I don’t know if the TBM was flying in frontal wx.
What worries me is that I encountered that rate of ice accretion in what looked a totally benign stratus cloud (NS obviously) with a 1500ft base and 4000ft top. -5C.
The other interesting thing about that PDF presentation Alexis posted above is that some of the types were out of control with just 1/6" of ice. I find that staggerring. How can something like that get certified? You can pick that up in the time it takes to type this sentence, just by flying through a “suitable” convective cloud.
The accident of the TBM developed and happened within 5 minutes … I don’t think that’s a long time. The only conclusion I can draw from this and the above presentation is: GET OUT as fast as possible, and most times it’s probably not a climb but a descent that will save you. It is interesting that the pilot reported only “light ice” but soon after he reported “rattling”… which could be a developing tail plane stall … it would fit that he stalled and lost control very soon after that.
I read through that presentation. Yes autopilot was sometimes an issue but more in the sense that the pilots didn’t have the sense to take over when it got really hairy. The biggest issue I saw was a lack of willingness to use and keep using anti and de ice protection in particular boots. The procedure for boots used to be weait until there was significant ice accumulation however this is now not the procedure recommended by the FAA – if ice is accumulating, you are supposed to use them. In the TBM, the rattle may well have been engine damage due to ice ingestion.
For the avoidance of doubt I am not suggesting being complacent at all. Just that excessive paranoia about autopilot in icing is misplaced. Even in a non-deiced plane, if you are building ice and in single pilot high workload situation, I would not just automatically reach for A/P disconnect. But of course, we can (and should) all make our own decisions on that.
My approach in anything other than trace icing:
In a climb, increase airspeed above minimum IAS for climb in icing conditions (135knots on mine)
Ensure anti-ice (pitot,stall,windshield,prop) is on and working
Monitor and assess changes using de-ice as appropriate.
No matter what don’t get too slow.
Well, then the people who sell these autopilots (and have no reason for hystery) are all paranoid if they tell you to NOT use the autopilot in icing conditions. What do you think why?
I will not use it, I know that now,
From FAA advisory 91-74
f.
Again, care should be exercised when using an autopilot in icing conditions, while in cruise, just as in other phases of flight. When the autopilot is engaged, it can mask changes in handling characteristics due to aerodynamic effects of icing that would be detected by the pilot if the airplane were being hand flown. In an aircraft that relies on aerodynamic balance for trim, the autopilot may mask control anomalies that would otherwise be detected at an early stage. If the aircraft has non-boosted controls, a situation may develop in which autopilot servo-control power is exceeded. The autopilot disconnects abruptly, and the pilot is suddenly confronted by an unexpected control deflection.
g.
Pilots may consider periodically disengaging the autopilot and hand flying the airplane when operating in icing conditions. If this is not desirable because of cockpit workload levels, pilots should monitor the autopilot closely for abnormal trim, trim rate, or airplane attitude. As ice accretes on aircraft without autothrottles, the autopilot will attempt to hold altitude without regard for airspeed, leading to a potential stall situation.
The whole documnet can be downloaded here: http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/74471
And from the DFC90 manual:
Envelope Protection During Icing Conditions The DFC90 autopilot is not to be used during icing conditions. The autopilot does not have any kind of AOA or icing input and therefore does not register changing aircraft dynamics during icing conditions. Therefore, Envelope Protection (EP™) is not effective under icing conditions.
That FAA advice makes sense. Sometimes these manuals are written for liability reasons rather than practical ones.
Of course the manufacturers are careful. But I ask myself: Why are they careful if it was a safe thing to do? I am pretty sure that they would not put that into the POH if there was no risk …
Maybe I am too careful. But I was never bold either.
The AP usage is NOT prohibited in icing conditions in the Cirrus with the GFC700 AP. That is what I stated above. It is only prohibited when the TKS system can not handle the ice anymore. That is in the FIKI approved aircraft version. Now, when in icing conditions, I do use the autopilot on IAS mode and I keep the speed higher than normal, which is also stated in the Cirrus Icing Awareness Course material. So, I keep the speed higher than normal and climb out and look at my climb ratio and look at the wings and the ice buildup (or not). Now: this is flying in icing conditions if I do note some ice, but that is something different than flying in severe icing conditions. As long as the Cirrus can handle the ice in normal TKS mode, I will leave the AP on and continue to focus on monitoring what is going on.
