737NG CFM engine temperature drop

[airpasty]

Does anyone know how much the temperature drops in the inlet of a CFM or similar jet engine? I work in China and they insist that engine anti ice isn’t mandatory at 10 degrees C, I know it’s unbelievable but I’d like to give them some “evidence” thanks

[gearlever]

Does anyone know how much the temperature drops in the inlet of a CFM or similar jet engine? I work in China and they insist that engine anti ice isn’t mandatory at 10 degrees C, I know it’s unbelievable but I’d like to give them some “evidence” thanks

Who is "they" ?

[airpasty]

Our Chinese line training instructors。。。

[Flying Wild]

Our Chinese line training instructors。。。
Hardly wise trying to point score with them...

[gearlever]

Considerations for flight crews (https://www.boeing.com/commercial/aeromagazine/articles/2010_q4/2/)

Have fun with your "instructors".

[excrab]

As Flying wild said. Just nod your head and agree, and take the money.
after all how many times have you got distracted, or had a sudden drop in temperature, and not switched it on until maybe +5 or + 6, and how many times have the engines stopped as a result? If you’re anything like me then the answers will be a few times and never, so it’s probably not worth stressing if they want you to turn it on at 9 degrees instead of ten.

[lomapaseo]

are we talking in the air or on the ground?

on the ground the air is sucked, in the air it's rammed. The 10C limit is close enough to be safe. Play with it and you take your chances with engine icing while in visible precip (snow, ice, fog, rain).

I suppose that if you define all the condtitions somebody could make a calculation of temp along the surfaces in an inlet and the fan blades

[yoko1]

Much less harm is done by having TAI on at 11 degrees than off at 9 degrees. YMMV.

[FlyingStone]

Does anyone know how much the temperature drops in the inlet of a CFM or similar jet engine? I work in China and they insist that engine anti ice isn’t mandatory at 10 degrees C, I know it’s unbelievable but I’d like to give them some “evidence” thanks

FCOM is very clear. And if they insist... well, you know why you're getting paid all that money.

[airpasty]

Thank you all. After 3 years of flying here it’s more to convince the future generation of FO’s that it’s not a good idea, apart from that I keep my head down but alas my desire to fix things gets in the way...

[safelife]

I did ice up like hell with TAT +11°.
Cross-checked with the other TAT sensor.
With CFM 56. In China.

[Dave Therhino]

My understanding is that the requirement to turn on cowl (inlet lip) anti-ice, which also raises the idle setting, at temperatures above 0C TAT has more to do with the indicated TAT range at which you can have supercooled water droplets due to atmospheric convective or precipitation action and the difference between OAT and TAT rather than any temperature drop the air experiences passing through the inlet. As said above, in high speed flight and in low speed low power flight the air temperature rises slightly as it slows down in the inlet.

[lomapaseo]

Again the original OP never defined the operating conditions regarding flight e.g. are we ramming air (in-flight) or sucking air (on taxi out or in.) and where is the ice assumed to be forming (on the inlet surfaces or on the engine surfaces). There are different levels of protection involved.

[tdracer]

Again the original OP never defined the operating conditions regarding flight e.g. are we ramming air (in-flight) or sucking air (on taxi out or in.) and where is the ice assumed to be forming (on the inlet surfaces or on the engine surfaces). There are different levels of protection involved.

Exactly - the risk of inlet icing is dependent on not only the air temperature, but on the airspeed and the engine power setting. At low speed, the air going in the inlet speeds up and cools, while at higher airspeeds the air slows down and warms passing through the inlet, with the amount of that heating or cooling related to the engine power setting. +10 deg. C protects for most foreseeable conditions where water/supercooled droplets could cause icing, without requiring the pilots to look up on a complex chart to see if there is a risk of icing.

In flight, (at least on Boeing), selecting engine anti-ice increases the idle speed to insure the bleed air used for anti-ice is warm enough, with enough pressure to do the anti-ice job.

[lomapaseo]

Just to add, after reviewing the early historical records of engine related icing, the safety gurus in the industry took note of the variances between manufacturers, AC and engines regarding ambient temperature "limits" in precips (we hadn't known about super-cooled at that early time). Indeed these early limits did vary by 5 degree C. The decision was made to harmonize at +10C to avoid confusing pilots transferring between products. This decision seems to have worked out well where it has been followed and is embraced uniformly

[airpasty]

Thanks for the info, I was mainly referring to takeoff as this is where they tell the FO’s it’s not necessary but as you correctly point out, this is where the temperature drop is at its greatest

[B737900er]

Simply show them FCOM 1. It clearly says when TAI is required.