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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

They only give you the the temp and dewpoint to assess the chance of mist forming.

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? :)

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 15°C. 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.

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"). :ok:

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.

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.

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.

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.

16-65 and 94 is correct but do you remember all the things done along the way.

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. :D

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.

The Hercs I fly (L382G) have a "Ground Start" position marked on the throttle quadrant.

Ground Idle - Ground Start Throttle positions
 

Hi Andrew

I am a bit confused. (Some might ask what's new). Are you saying that the L382G you operate has both a Ground Idle and a Ground Start position on the throttle quadrant? Ground Idle is the normal throttle position for start on the models I operated on. It gave/gives minimum blade angle to minimize starter load and to assist in smooth acceleration to ground idle RPM after starter cut-out. Have never seen a Ground Start position labelled on a C130. If you have it, is it slightly behind the Ground Idle detent?

"Ground Idle" - (Approximately 10 degrees coordinator travel) is a detent position. This is the ground operating position at which blade angle is set for minimum thrust.
"Ground Start" - (Approximately 18 degrees coordinator travel) is a detent position. This position sets blade angle for engine starting.

Maybe it is G model stuff only. Less blade angle drag. Probably would work with the older models as well(at leat with 54H60 props) but no detent for positioning the throttle, only guesswork.

Yep, both are marked on the quadrant. Like Jammed Stab pointed out, the Ground Start position is just ahead of the Ground Idle position.

For what it's worth, on the L382 the "G" designation only has to do with the fuselage length not the production series. An L382G is one with 2 fuselage plugs (180 inch total stretch) either when built or as a retrofit. Also called the L100-30 A short fuselage plane would be a L382B (L100) and one with a single 100 inch stretch would be an L382E or F (L100-20)

All our planes are L382G's but some have GTCs and some have APUs which if I'm not mistaken, makes then equivalent to the C-130E and C-130H respectively.

In Europe most airports give you the OAT with the start clearance. In the last 39 years I have NEVER heard the dew point mentioned, except on ATIS.

All engines have min and max OAT's for start. Perhaps it is related to that?

Yes, You are right. But here at Mar del Plata Airport we don´t have ATIS Information. The MET office give us the METAR and we tell to every aircraft incoming or outgoing the information.

So the critical point of the OAT is below 10°C and/or with a narrow temp/dew pt spread?? No matter if the aircraft has FADEC or not, or autostart or not??

Some kind of flameout? or a hot start, right?

So. I understand at a high N1 Percent??

APU is better, much better.

Especially in the Desert.

The shafts are not all named the same on individual engines. Typically, the high pressure compressor shaft is the one the starter acts upon (if there is more than one shaft installed, of course). So the relevant number is usually N2, Nh (on the PW120 series) or whatever else the high pressure spool RPM figure may be called in the individual engine. There may be limitations involving other spools: for example on the RR Tay engine, N1 rotation must be indicated before the fuel levers may be opened.

When starting the engine, not only the compressors have to come up to speed, but also the normal gas flow pattern in the engine has to be established. A strong tailwind will increase the pressure the hot gas flow has to overcome when leaving the engine, and also (try to) spin the fan backwards, thereby applying some adverse/opposite torque to the respective turbine, resulting in more drag that also needs to be overpowered by the gas flow. Generally, higher drag and slower turbine speeds will lead to higher exhaust gas temperatures (nicely visible on a turboprop: an identical power setting will show higher EGTs with lower prop RPM and vv.). So the flameout is not really a problem, but a hot start definitely is.

It seems that You are after the definition of icing conditions here - those are relevant for takeoff, but only rarely for engine startup. The exact definition varies a bit by aircraft type: on the Fokker 70/100, it is "OAT below +5°C AND spread below 3°C", on the DH8 on the ground, it is OAT at or below 10°C AND visible moisture (i. e. precipitation of any kind, drifting or blowing snow or the like, or mist with visibility below 1600m). So it is not really possible to give You an answer suiting all types, engines and also operators.

Ground Start/Ground Idle Detents
 

JS & AA. Had a busy day and only just able to respond. You point out that you have a Ground Idle position at about 10 degrees throttle position and a Ground Start (with Detent) at 18 degrees.

As I said, none of the Military C130's (A-E-H) that I operated on had a Ground Start throttle position. Ground Idle is a detent position at 18 degrees, which lines up with where you reckon you have a Ground Start detent. I can't fathom why you would then have a ground idle position a further 8 degrees back toward Reverse. As a matter of interest do you start in Low Speed Ground Idle or Normal?

And yes, I also reckon the APU was a much better setup than having the GTC/ATM combo.

I think CFM 56 are certified to start up to 60 kts TW,not like i ever tried:p

I can't say really. Honestly I didn't know that the military Hercs were different. I will say that the 18 degree detent (ground start on the L382) is not a neutral thrust position. A light plane on level ground will roll along quite nicely with the throttles in that position. The Neutral thrust position for the throttles would be a bit aft of that detent, about where "ground Idle" is marked on the quadrant.



LSGI. Unless the engineer forgets to punch the buttons before start. Then we start the other three in LSGI after he pushes the buttons down. Then he buys the beer after the flight.

GI/GS
 

AA Don't doubt your word for a second mate. I know the aircraft will taxy easily without any movement from GI and, especially on the A model with no LSGI a tad of throttle position aft of GI was needed to control taxy speed on flat taxiways.

Only problem which needed to be mindful of was that the oil temps can come up quickly in hot wx. Doesn't take too much to get to 100 C.

Hope you guys can continue in the Lockheed Legend for many years to come!!