B757 and Freezing Rain

[hoey5o]

So can anyone comment on whether the B757 (uk based) is allowed to operate in freezing rain as getting an authoritive yeh or neh seems a little difficult at the moment. I believe the UK CAA dont approve any commercial aircraft for severe icing but I may be wrong. Perhaps Boeing/FAA approve ? The manuals dont seem to mention it.

[Daysleeper]

The whole point of the term "severe" in relation to icing is

The rate of ice accumulation on an aircraft is such that de-icing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.

from the NOAA website.

So flying in Severe icing is unlikely to be a long term problem as you have the aerodynamic efficiency of an iceberg.

As for freezing rain specifically if you look at the hold over times for "light"

Type 1 : 02-05
Type 2 : 10-30
Type 2 : 05-40

times in minutes depending on OAT. So there really is very little protection avaliable, and as soon as it goes "moderate" then there are no holdover times and your grounded.

[hoey5o]

Well thanks for that Daysleeper, now is there anyone who can actually answer the question; are 757's approved to FLY in freezing rain ? Perhaps someone with a UK operator has it in their ops manual or maybe someone has access to the original AFM.

[captjns]

Originally Posted by hoey5o

So can anyone comment on whether the B757 (uk based) is allowed to operate in freezing rain as getting an authoritive yeh or neh seems a little difficult at the moment. I believe the UK CAA dont approve any commercial aircraft for severe icing but I may be wrong. Perhaps Boeing/FAA approve ? The manuals dont seem to mention it.

Like all transport category transport aircraft, the B757 was certified by the FAA to fly through known icing. The WTAI system is able to cope with server icing conditions for a limited period of time however. I have not come across any limitations regarding operating in severe icing conditions. The engines whether P&W or RR are subject to vibration when the fan blades accumulate icing do to the fan blade balance. Here is an excerpt from the Boeing 757 AFM which refers to Engine Anti Icing. I have the AFM on my computer. However unfortunately, I can’t copy it since it is copy write protected.

Anyway here it is word for word:

“NOTE: Under all but very server icing conditions, ice will shed when thrust is reduced to idle, eliminating the need for the need to subsequently apply higher than desired thrust.”

Perhaps specific operators insert provisions regarding prohibited operations in severe icing all together. Regardless of what the manual says, if possible, the safest operating procedure is to avoid moderate to server icing conditions.

I hope this was of some help to you.

[Daysleeper]

Without being overly touchy your question was

can anyone comment on whether the B757 (uk based) is allowed to operate in freezing rain

I'm not surprised your struggling to get a definitive answer if your not sure what your asking.


As to "are you approved to FLY in freezing rain": the aeroplane is certified for flight in known icing, there is no difference made between icing caused by freezing rain or icing caused by any other means.....however as freezing rain often results in icing which exceedes the capability of the aircraft systems to shed (the definition of severe) you would be ill advised to continue flight in such conditions and if you did continue flying in such conditions it probably would not be for long anyhow.

[Ice-bore]

Originally Posted by hoey5o

So can anyone comment on whether the B757 (uk based) is allowed to operate in freezing rain as getting an authoritive yeh or neh seems a little difficult at the moment. I believe the UK CAA dont approve any commercial aircraft for severe icing but I may be wrong. Perhaps Boeing/FAA approve ? The manuals dont seem to mention it.

The FAA state on page 10 in FSAT 05-02, "..NOTE: The FAA does not approve takeoff in conditions of moderate or heavy freezing rain."

[hoey5o]

Thanks IceBore,

I suspected as much, would also like to see it in a UK ops manual somewhere. In a previous airline with several different types they also had a blanket ban on ops in freezing rain full stop.