737 Emergency descent and anti ice
Thread Starter
737 Emergency descent and anti ice
There is a sentence in the emergency descent checklist that I am not 100% sure I understand. The sentence is " Reduce thrust to minimum or as needed for anti-ice".
My understanding is that in many circumstances anti-ice would not be in use so thrust would be at minimum ( every sim I have done) , however, if anti-ice was needed and the COWL VALVE OPEN light remained bright blue, and an amber TAI was indicated, thrust should be increased only enough to have the COWL VALVE OPEN light go to dim ( and the amber TAI return to green ).
Does that sound like a fair interpretation of the sentence? It seems very unlikely to me that the light would remain bright and the Amber TAI would illuminate as I have never seen this on line ops, is it a case of Boeing covering a very unlikely scenario by adding a sentence to the memory items?
Thanks,
Qanda
My understanding is that in many circumstances anti-ice would not be in use so thrust would be at minimum ( every sim I have done) , however, if anti-ice was needed and the COWL VALVE OPEN light remained bright blue, and an amber TAI was indicated, thrust should be increased only enough to have the COWL VALVE OPEN light go to dim ( and the amber TAI return to green ).
Does that sound like a fair interpretation of the sentence? It seems very unlikely to me that the light would remain bright and the Amber TAI would illuminate as I have never seen this on line ops, is it a case of Boeing covering a very unlikely scenario by adding a sentence to the memory items?
Thanks,
Qanda
Dutch Roller
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Had exactly the same question during prep for a sim check. Asked our technical pilot and he got this response from Boeing:
Quote:
"The intent of the step is to maintain adequate thrust to ensure the engine anti-ice valves are open. If the thrust is adequate, the amber TAI indications on the upper DU are not displayed and the COWL VALVE OPEN lights are illuminated dim. If the amber TAI indications on the upper DU display and the COWL VALVE OPEN lights remain illuminated bright with the engines at idle, the thrust should be increased slightly to an approximate minimum of 30% N1, which is the nominal threshold to open the engine anti-ice valves. The step also serves the purpose of drawing crew attention to the possible need for engine anti-ice."
Like you I have never seen an amber TAI because of low thrust but apparently it could happen.
Quote:
"The intent of the step is to maintain adequate thrust to ensure the engine anti-ice valves are open. If the thrust is adequate, the amber TAI indications on the upper DU are not displayed and the COWL VALVE OPEN lights are illuminated dim. If the amber TAI indications on the upper DU display and the COWL VALVE OPEN lights remain illuminated bright with the engines at idle, the thrust should be increased slightly to an approximate minimum of 30% N1, which is the nominal threshold to open the engine anti-ice valves. The step also serves the purpose of drawing crew attention to the possible need for engine anti-ice."
Like you I have never seen an amber TAI because of low thrust but apparently it could happen.
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Some MEL items require a minimum thrust setting when anti ice is needed! That's what that sentence in the emergency descent pertains to! For example MEL 30-03-03 in the operations note it says to maintain a minimum of 60% N1 during flight in icing conditions. Has been discussed before.
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Flight idle on B737 Classic ( and I seem to remember also on NG) always gives you more than 30%N1 through Flight Idle. ( thrust does not increase with EAI ON by the way) Only if for one reason or another you have Ground Idle ( MEC/EEC related mostly), there is a chance that you will get a bright blue EAI light, indicating a valve that is not in its correct position. I have seen this in operation indeed, but only on a couple of occasions during my 14 years on B737.
It is more prevalent during ground operations.
It is more prevalent during ground operations.
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My understanding is that some CFM 56 series engines are (were) not yet modified in cowl re-design (spinner and splitters) to combat very heavy rain or icing. Until those modifications were completed there was a placard to maintain a minimum of 45% N1 during idle descent for rain ingestion reasons. That was several years ago so no doubt the required modifications have been completed by now and thus the restriction has been removed
