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Temperature and Engine start!

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Temperature and Engine start!

Old 18th Feb 2014, 19:11
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Temperature and Engine start!

I have a question about why ATC should say the temperature and dew point before start up?? specially for jet airplanes! Is there a part of the start up precedure where the Temperature and dew point are crucial for jets?? Thanks in advance.
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Old 18th Feb 2014, 23:29
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I'm concerned with temperature and dew point during engine start only when less than 10C.

At that temp and lower (with a narrow temp/dew pt spread) there is a chance of localized icing (due to Bernoulli effect) and therefore anti-ice should be selected on.

In other cases (high ambient temps) there may be performance issues.

Sort of depends on local conditions and practices.
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Old 19th Feb 2014, 14:14
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i'm flying around in europe and ATC has never given me the temperature or an update on the temperature before startup. Of course you need to stay inside your environmental envelope and temperature is needed for various performance calculations, use of engine anti ice as pointed out be zerozero, etc. for engine start up itself i am more concerned about the wind direction since a strong tailwind might lead to a start malfunction.
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Old 19th Feb 2014, 16:53
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Originally Posted by M Invernoz View Post
I have a question about why ATC should say the temperature and dew point before start up?? specially for jet airplanes! Is there a part of the start up precedure where the Temperature and dew point are crucial for jets?? Thanks in advance.
The short answer is no. By the time you start you should have copied the ATIS long ago for whatever you needed those info. Rwy, wind, temp etc.
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Old 19th Feb 2014, 17:05
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Well, on some non-FADEC engines (PW123 for example) a high OAT in combination with a hot engine might lead to considering switching the fuel levers to on at a slightly higher compressor speed to keep the exhaust gas temperatures a bit lower - but this is no exact science and no exact figures are needed for this decision.
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Old 19th Feb 2014, 17:24
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Digressing from ATIS

When starting a Non FADEC hot engine the engine should be run to MAX motoring speed to cool the engine prior to selecting fuel, this could be as low as approx 100 deg C so high ambient temp will not really effect the starting cycle.
A FADEC engine would automatically do this for you.
For example I have timed a Trent 700 motoring for 40 seconds to reduce the internal temperature before fuel light off.
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Old 19th Feb 2014, 17:37
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Tinwacker, perhaps this is a nitpick, but it's not FADEC, it's Autostart that matters.

Not all FADEC have Autostart basic (e.g. PW4000/94" it requires an optional additional box).
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Old 19th Feb 2014, 21:28
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Tinwacker,

true, if the SOPs say so. On the DH8-300 (PW123) I flew a while ago, the book wanted us to switch on the fuel at 19% Nh for a hot engine, although the starter was capable of a bit more. And on the F70/100 (RR Tay 620/650), the books call for maximum motoring N2 was not connected to a warm engine, but to strong tailwinds spinning N1 in opposite direction. This is why I hesitated a bit to write "it is thus every time and on every type". Of course, SOPs rule and every engine has its little peculiarities.
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Old 19th Feb 2014, 21:39
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I my experience, they only tell you temp/dewpoint if there has been a change from ATIS (which may be a few hours old at some smaller airports or non-busy times like 4am), or if there is no ATIS. So they just give it to you as a courtesy for performance planning for take-off, otherwise you are going to ask them for it anyway.
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Old 20th Feb 2014, 08:37
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M Invernoz

As you can see from most replies, in most places they no longer give you this information before start. But yes they still do all over Africa and I suppose in Argentina as well. It is outdated and will disappear but I can't tell you why they ever did it in the first place.
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Old 20th Feb 2014, 08:53
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They only give you the the temp and dewpoint to assess the chance of mist forming.
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Old 20th Feb 2014, 23:29
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If OAT= dew point, perhaps they're concerned, if you're starting engines with intent to fly, that you/the airframe/the airfield are LVP qualified?
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Old 21st Feb 2014, 02:21
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Temperature can be a factor. I have seen two turbine engines where OAT had to be taken into consideration. The -9 and -9A versions of the JT8D had different max start temps depending on whether the OAT was above or below 15C. The Dart engine, at least on the aircraft I flew, had different fuel trimmer settings for start and takeoff depending on OAT.

But I have never heard ATC giving the temperature to pilots as what would appear to be a policy when pushback or engine start was requested.
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Old 21st Feb 2014, 17:48
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I have had more hot starts with JT9's during cold weather ops than with summer ambient temps. In that engine, at least, when you turn the fuel on (idle/rich) is dependent on EGT. Max motoring may go beyond just an N2 RPM if the EGT is above 100dC. The only influence reported temperature has is whether engine anti-ice is required after start.

Tailwinds, in my experience, didn't seem to have a big effect, if any, on JT9 starting temps, which was good with engine pneumatic air required for reverser deployment preventing reversers use during start. Hydraulic reversers are desired, at least for the placebo effect of blocking the tailwind during start and a quieter preflight experience (not only quiet, its also easier to preflight the fan blades when they aren't rotating at "max motor").

The Herc, as I recall, was more sensitive to strong tailwind starts. Lowering flaps to 100% in order to reduce wind up the tailpipe helped to control starting temps. A speed sense switch controlled the start sequence of fuel and ignition, so there wasn't much else the crew could do other than to release the start switch at the recommended RPM and hope for the best that everything worked as advertised.
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Old 22nd Feb 2014, 05:14
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Allison Start Sequence

16% - 65% - 94% still sticks in the memory bank. The C130A and C130E starter switch were held in the start position by a solenoid and auto released at around 52% RPM. If it did not the switch had to be manually released. The H model used a toggle switch to open the Starter valve, held in the open position manually against spring tension and released at around 60% RPM. Rather than just sit back and "hope for the best" if a hot start or stagnated start occurred it was simply aborted by using the condition lever to GROUND STOP. Strong tail winds did potentially lead to hot starts.
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Old 22nd Feb 2014, 10:55
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The JT-8 on B732 was indeed one case of needing to know this. It was the norm at LTN, being the BY main base of the ubiquitous B732 squadron, for ATC to give OAT with start up; not the dew point. Over the past 20 years, since I and the world moved on, I've not noticed it anymore in many countries. I wonder if Turbo-props still need this data.
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Old 22nd Feb 2014, 14:04
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Originally Posted by Desert185 View Post
I have had more hot starts with JT9's during cold weather ops than with summer ambient temps. In that engine, at least, when you turn the fuel on (idle/rich) is dependent on EGT. Max motoring may go beyond just an N2 RPM if the EGT is above 100dC. The only influence reported temperature has is whether engine anti-ice is required after start.

Tailwinds, in my experience, didn't seem to have a big effect, if any, on JT9 starting temps, which was good with engine pneumatic air required for reverser deployment preventing reversers use during start. Hydraulic reversers are desired, at least for the placebo effect of blocking the tailwind during start and a quieter preflight experience (not only quiet, its also easier to preflight the fan blades when they aren't rotating at "max motor").

The Herc, as I recall, was more sensitive to strong tailwind starts. Lowering flaps to 100% in order to reduce wind up the tailpipe helped to control starting temps. A speed sense switch controlled the start sequence of fuel and ignition, so there wasn't much else the crew could do other than to release the start switch at the recommended RPM and hope for the best that everything worked as advertised.
Yes, the Allisons on the Herc were much more temp sensitive. On a hot day, especially at altitude, it could be a good idea to get positioned into wind and make sure the throttle was properly positioned for min blade angle. I have seen aborted starts due to stagnating rpm because they were at ground idle instead of ground start position. I suppose if you were using fuel enrichment, that could make a hotter start.

Flaps 100% is an interesting idea but how do you get them therefor the first engine start if this wasn't anticipated on the inbound leg. 9 port valve selector to interconnect systems?

As for the bigger engines you mention, I have seen a 40 gust 50 tailwind(at the end of a typhoon) on a warm day start on the CF-6 with its EEC's having no problem controlling temperature.

Originally Posted by Old Fella View Post
16% - 65% - 94% still sticks in the memory bank. The H model used a toggle switch to open the Starter valve, held in the open position manually against spring tension and released at around 60% RPM. Rather than just sit back and "hope for the best" if a hot start or stagnated start occurred it was simply aborted by using the condition lever to GROUND STOP. Strong tail winds did potentially lead to hot starts.
16-65 and 94 is correct but do you remember all the things done along the way.
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Old 22nd Feb 2014, 22:50
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Flaps 100% is an interesting idea but how do you get them therefor the first engine start if this wasn't anticipated on the inbound leg. 9 port valve selector to interconnect systems?
We normally left them at 50% after landing. If the tailwind was quartering, start the engine masked by the fuselage, hopefully #2, which would provide Utility system hydraulics. Drop flaps to 100%, and start remaining engines. If you were the crew for the next impending leg, just leave flaps at 100%. It did help...

"Flaps" was on the Before Takeoff Checklist, so no worries on flap position for takeoff.

I flew civilian G models and one E we had for awhile. Not glamorous like the Jet God types, but we had a great time flying the manly airplane, while hauling expensive trash all over the world.
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Old 23rd Feb 2014, 02:13
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Remember what happens.

As a matter of fact I do JS. 16% RPM:: "Enrichment" if selected/"Fuel Flow" if not, "Ignition", "Oil Pressures", "Hydraulic Pressure", "Parallel" (Engine driven Fuel Pump to Parallel for greater volume at low RPM) Starter Button out by 52-54% or Start Valve Switch to off by 60%. 65% RPM:: "Series" ED Fuel pump to Series operation, Ignition OFF 94% RPM:: "Peak T.I.T....." (830 degrees C Max Normal) 5th & 10th Stage Acceleration Bleed Valves close. On the T56A-11 fitted to the C130A's I operated there was no Low Speed Ground Idle as the 5th & 10th Stage Bleeds were not ducted overboard, simply discharged into the nacelle, so any failure of a Speed Sensing Switch to below 94% led to a Nacelle Overheat very quickly. We also had optical Fire Detection sensors in the A model which were prone to giving false Engine Fire Warnings. Thread drift I guess, but I enjoy the memories of the old girls.

BTW JS, I don't know which C130 you operated, but none of the three models I was on (A-E-H) had a "Ground Start" position on the throttle. Max Reverse - Ground Idle (detented) - Flight Idle (Over the Step) - Take-Off were the only marked positions. Condition Lever to Run - Throttle at Ground Idle were the respective positions for Ground start.

Last edited by Old Fella; 23rd Feb 2014 at 02:50. Reason: Correction to text
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Old 23rd Feb 2014, 07:19
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Originally Posted by Old Fella View Post
BTW JS, I don't know which C130 you operated, but none of the three models I was on (A-E-H) had a "Ground Start" position on the throttle.
The Hercs I fly (L382G) have a "Ground Start" position marked on the throttle quadrant.
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