Outside air temp to turbines

[Lissart]

Evening.


The Good and Holy Book of UK ATC (MATS1) requires us to pass the outside air temperature to turbine aircraft on request of start-up. Why? Apart from the fact that it says so - therefore just do it! None of the pilots I have questioned on this can answer me and moreover they are not the slightest bit interested. Regrettably, there have been occasions when one has forgotten to pass the temp (fading neurones) and not once ever has a pilot asked for it!! Google was less than helpful with a load of stuff I struggled to understand about needing to heat air passing through the engine and as it gets colder needing more energy - therefore fuel to do this. But given our gloriously mild climate I have difficulty accepting this as a plausible excuse. Thoughts?


Respectfully Yours.

[4Screwaircrew]

A long time ago I flew aircraft with RR Darts, we were required to preset the fuel trim for start according to the OAT, maybe this goes back to the days of those early turbines which lack the sophistication and automation of the engines that came after them.

[dixi188]

The RR Spey had a "Start" and "Run" position on the Fuel Cock. Below a certain temp. the start position would be used initially to provide more fuel during start, then the lever was moved to Run. Above this temp the lever would be put straight to Run.
It may have been 10 C but I'm not sure. It's been about 30 years since I last ran a Spey.

Also as 4Screwaircrew says, the RR Dart required trim setting, but I think we used to set 75% for start and then trim back to control the temp during the start.
After start the trim was set for take off using a small rotary slide rule (called the "Trim Computer") to calculate the correct figure using temp. and pressure alt.

[Lissart]

Thanks chaps! That is just the sort of once-upon-a-time stuff I was looking for. I suppose it is the same as the way technology has developed with our cars - who has a manual choke these days?


Regards.

[LMX]

The 737s I fly still require a manual temperature input in the FMC for performance calculations. So if there's no ATIS I would ask ATC if not provided at the request of "departure information ".

[2 sheds]

Lissart
Why are you so concerned? You would only pass that information anyway in the absence of the pilot acknowledging the current ATIS.
2 s

[Lissart]

2Sheds - Aren't you assuming there is an ATIS...? (There isn't where I am.) Just common curiosity on my part having a/. an interest in aviation and b/. a wider view of the world than just mindlessly following what it says in some manual. You must remember the days when we were allowed/supposed to think outside the box? Given the wording of my post and the subsequent helpful responses, I see little reason for your tone. Questions are still allowed, as is curiosity. Indeed after an interregnum away from ATC I see we now have more emphasis on Human Factors etc which to me says that the human organism - it's rhythms, capacities, strengths and weaknesses - is being addressed in a way similar to that which is now common place in the piloting community. (About time.) So maybe the "caustic controller" and the "caustic OJTI" will be a thing of the past like the "caustic captain" on the flight deck. I've seen both the two former where any sort of enquiring mind was treated in an arrogant and disdainful manner and where - for example - the perfectly right and proper desire of a trainee to ask even simple questions was fraught with the risk of being torn off a strip. Why am I so concerned? Why not for Heavens' Sake?? (Thread drift I appreciate......)

[dixi188]

Another story.
In Sharjah one day about 1400 local, RTOM had been calculated using the ATIS temp. Fuel and cargo loaded to the limit, called for start to find temp had gone up a few degrees and now we were over weight. Off loaded some cargo and now ready to go. Called for start to find temp had dropped a bit and cargo could now be carried.
We left it behind as time was wasting.

[2 sheds]

Lissart - Ouch! No "tone" intended, I assure you. Let me re-phrase it - ATC would only pass that information anyway in the absence of the pilot's acknowledgement of ATIS - if one has ATIS at one's aerodrome, of course! You do, however, refer to MATS 1 in slightly disparaging terms - the direct answer to your original question is that it is in MATS 1 because it is specified by ICAO in PANS-ATM.
2 s

[Lissart]

2 Sheds,


If I have inadvertently refer to Our Beloved Bible in disparaging terms I should be struck off! I have no doubt that in certain circumstances as quoted by responders the passing of temp has a relevance. However, Dixi is referring to conditions where perf is highly likely to be limited by very high temps and the previous two examples are probably from a by-gone age. (Anyway, surely pistons at high temps also need the figure for perf reasons where air density might be an issue.) It is just that the turbine types that use our place have no interest in the air temp, as clearly their FMS does not require it and with electrical engine management these days fuel management relative to temp is auto. Even the Chief Pilot could not think up a reason why he would want to know! So I wondered you see... [How much of MATS1 is specified - or not - by PANS-ATM?!!]

[Rwy1234]

Oh Lissart, thank you for laughs!