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Hot Start On Engines, What Next?  
User currently offlineTrent_800 From United Kingdom, joined Jan 2002, 136 posts, RR: 0
Posted (12 years 4 months 5 days 8 hours ago) and read 5420 times:

When starting a Engine up and the crew notice that the fuel flow is above normal and the EGT keeps rising and rising the pilot cuts the fuel flow to the engine to prevent a meltdown. My question is what happens next? Does the pilot let the engine settle and try to start it again or does one would-be hot start warrant the engineers to be called in?

54 replies: All unread, showing first 25:
 
User currently offlineBjones From United States of America, joined Feb 2002, 123 posts, RR: 0
Reply 1, posted (12 years 4 months 5 days 5 hours ago) and read 5277 times:

It really depends on a lot of things. How hot it got (were any limits exceeded), what aircraft/engine you have, why you think it got hot. In some aircraft there are certain things that contribute to hot starts that can be compensated for. For instance some small jets with electric starter motors instead of air starts might have a weak battery which caused a slow spool up, this could be remedied by using an APU. In other cases the hot start might be due to a hot day with a wind blowing the exhaust gas back up the tail pipe. Or of course it could be a aircraft malfunction. Typically if you exceed any operating limitations or see something such as very rapid ITT or EGT(depending on acft type) rise its time for maintenance to look at the aircraft the first time.

User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 2, posted (12 years 4 months 5 days 1 hour ago) and read 5196 times:

A generic QRH procedure would be, for a rapidly rising EGT/ITT (or Turbine inlet temp, whatever is specified for the particular engine):

1. Abort the start; if ITT remains high,
2. Dry motor the engine
3. If a temp limit was exceeded, call maint for an inspection or additional procedures

If temp limits weren't exceeded, and after the engine has been motored, another start attempt is typically OK.

Finally, it's hard gauge a start by monitoring fuel flow, as it will vary with atmospheric conditions and the rate at which the engine accelerates. Generally EGT is the primary parameter, with N1, oil pressure, ignitors, and fuel flow all being secondary to temp.


User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 3, posted (12 years 4 months 4 days 3 hours ago) and read 5105 times:

Typically, a hot start will be preceded by abnormally very high fuel flow when the fuel lever (switch) is raised.




You're only as good as your last departure.
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 4, posted (12 years 4 months 3 days 16 hours ago) and read 5061 times:

Fuel flow is your first indication of a possible hot start. I'm not saying you're going to get one, but I typically watch a little closer to prevent the hot start.

User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 5, posted (12 years 4 months 3 days 15 hours ago) and read 5058 times:

I don't agree...I've never seen a max fuel flow limitation as part of a start procedure. Fuel flow will vary with atmospheric conditions, whether its a mechanical fuel control or FADEC equipped.

From the above viewpoint, if a rapidly rising fuel flow is the "first indication of a possible hot start", and the resulting start is normal, then what value is fuel flow as a first indication? It's not; EGT is.


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 6, posted (12 years 4 months 3 days 15 hours ago) and read 5050 times:

A hot start can also be preceded by a slower than usual N1 acceleration, but again the primary parameter is egt.

User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 7, posted (12 years 4 months 3 days 14 hours ago) and read 5044 times:

There is a specified fuel flow range for engine start. The JT9D-7AH's range is 600 - 800 pph. Anything above 800 pph should be viewed as having the possibility of a hot start.



User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 8, posted (12 years 4 months 3 days 5 hours ago) and read 5024 times:

Every gas turbine has a range of normal startup parameters from oil pressure to vibes to N1, N2 etc.
What does "anything above 800 lbs/hr should be viewed as having the possibility" mean? That doesn't sound like a limitation...

Fuel flow is a secondary, not the primary or "first" indication of a hot start.


User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 9, posted (12 years 4 months 2 days 16 hours ago) and read 4989 times:

A300/310 Run/Taxi Study Guide

Hot Start (A300-600 w/GE CF6-80
A hot start can be anticipated by observing an initial fuel flow greater than normal (greater than 700 pounds/hour) at the instant the HP fuel lever is placed in the position. After light off, fuel flow will rise as needed to accelerate the engine to idle RPM. Normally this will be about 1600 PPH peak but will vary depending on weather conditions.

If hot start occurs, terminate starting cycle immediately by returning HP fuel lever to OFF position. Continue motoring engine to reduce EGT below 180 degrees C. If light off did not occur spool engine for 30 seconds to purge engine of excess fuel.

CAUTION
Do not attempt a second start if fuel flow on initial start (prior to light-off) was above 700 PPH, or if maximum motoring speed was below 15% N2 or damage to engine could result.



You're only as good as your last departure.
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 10, posted (12 years 4 months 2 days 16 hours ago) and read 4985 times:

The 600-800pph is straight from the maintenance manual. A higher than normal fuel flow at "fuel on" can indicate the possibility of a hot start. It is not an absolute that high initial FF will induce a hot start. In fact most starts go normal. But, I have never had a hot start (or actually an impending hot start) without the fuel flow being higher than normal at fuel on.

If you look strictly at EGT you are already behind the 8-ball. You have to look at all the parameters and make your conclusion based on what you see. A spiking EGT does not mean hot start, in fact the -7AH EGT goes like a bat out of hell to about 550c then settles out and rolls back. On hot days it may go to 600c. The limit is 650c.

You are correct that FF is a secondary engine indication, but is the first indication you will see that gives you a clue as to the health of the engine fuel system.


User currently offlineL-188 From United States of America, joined Jul 1999, 29791 posts, RR: 58
Reply 11, posted (12 years 4 months 2 days 11 hours ago) and read 4971 times:

This probably not in the book. But back in the day this used to be a really common occurance on a certian turboprop engine in cold weather say in the -20 -30 ambient range.

We called it a Garrett pre-heat. Usually the second attempt the oil would be fluid enough to get the engine to go.

I think the feds and the engine manufactures frown on this practice however.



OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 12, posted (12 years 4 months 2 days 4 hours ago) and read 4949 times:

So do you abort the A310 start at 710 lbs per hr if everything else is normal. No; so that's not a hard limit, but it could be a secondary indication, as I've said.

My original objection was that fuel flow is the "first indication of a hot start."

By the above scenario, clearly it's not.

I've stated many times that secondary parameters (other than egt) should be in the start up scan.


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 13, posted (12 years 4 months 2 days 4 hours ago) and read 4950 times:

Also-

A spiking EGT should trigger an aborted start, which lends to the def of EGT as the primary, and in many cases, sole indicator of a hot start.

A rapidly rising fuel flow? Not necessarliy does the start have to be aborted; it must be compared to the other parameters.


User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 14, posted (12 years 4 months 1 day 22 hours ago) and read 4931 times:

Excessive fuel flow during initial fuel application, as spelled out by the engine makers and adopted by the airlines is the prime precurser of a hot start.

If, as you ask, do you abort the start when fuel flow goes to 710 PPH but everything else is normal? YES. Remember this is an instantaneous 710 PPH.

An analogy to that example would be, "On taxi out,do I stop extending the flaps because I heard ripping and crunching noises or should I try the next detent and see if the noise stops?

First off, how do you determine everything else is normal. This excessive fuel flow normally occurs before light-off.

The old saying, "an ounce of prevention is worth a pound of cure", rings true. Especially regarding hot starts.



You're only as good as your last departure.
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 15, posted (12 years 4 months 1 day 10 hours ago) and read 4915 times:

FDXmech,

Thanks for the assist. I guess us freight dogs can teach others, or have operated enough crap to understand what the engine is trying to tell us.


User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 16, posted (12 years 3 months 4 weeks 1 hour ago) and read 4885 times:

Air2gxs.... fellow freight dog here to corroborate your info as correct.

One of my companies procedural callouts on start is "FUEL FLOW: NORMAL/HIGH".

If the fuel flow is "high"we abort the start and call maintenance. Let them crank the fucker over.

Its all determined by each individual company prescribed in the AOM.

First indication to you that the engine may hotstart in chronological order is as follows.

1. Engine fails to meet minimum N2.
2. Fuel Flow abnormal
3. Excesive EGT rise.

If number 2, or 3 indication is present you have an "impending hot start" which there is a procedure for in the abnormal section of your AOM.

If an engine actually hotstarts... meaning you exceeded your max start EGT limitation then you were sleeping. Because and engine wont hot start without some abnormal indication.

JET





User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 17, posted (12 years 3 months 3 weeks 5 days 4 hours ago) and read 4847 times:

I still haven't seen fuel flow as a HARD limit in an FOM.

If everything else is normal, and fuel flow is high, (say 700 lbs/hr in the above ex), we start the engine. What "airlines" do is certainly not 100% standarized or compatible, as implied above.

All of the above verbage indicates higher fuel flows COULD be indicative of a hot start. That means it's subjective. As an engine approaches the need for an overhaul, startup fuel flows typically increase due to increased (greater than new spec) engine tolerances, dirty fuel nozzles, worn ignitors, etc.

For the above reasons, fuel flow can only be a secondary input to determining a hot start; not the primary.


User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 18, posted (12 years 3 months 3 weeks 4 days 20 hours ago) and read 4828 times:

I'm confused to what the actual debate is about, or are we talking semantics?

Let's clearly define the present point of contention.



You're only as good as your last departure.
User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 19, posted (12 years 3 months 3 weeks 4 days 17 hours ago) and read 4812 times:

I don't agree with the 4th post; for reasons I stated in the 5th and following posts and below:

1. A "possible indication" is NOT a limitation.
2. I've never seen a fuel flow (ie a specific value) as start limitation parameter.
3. For the above reasons, fuel flow can only be a secondary indication of a hot start.


User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 20, posted (12 years 3 months 3 weeks 4 days 16 hours ago) and read 4806 times:

You run engines your way and I'll runthem my way, which by the way is the way our AOMs, MMs & training manuals tell us to run them.



User currently offlineApathoid From , joined Dec 1969, posts, RR:
Reply 21, posted (12 years 3 months 3 weeks 4 days 16 hours ago) and read 4804 times:

...and the first time you turn a turbine into a slag pile you will come in and say "abnormally high fuel flow at light off really IS an indicator of a hot start."

High ff at light off should tell you to pay attention. No, it is not the ONLY sign, but it will be the first. Every mechanic I know uses that call out during light off.

Until you come up with a good reason NOT to monitor ff, can you at least admit its not a bad idea.


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 22, posted (12 years 3 months 3 weeks 4 days 16 hours ago) and read 4801 times:

Have you not read a thing I've written????

Can you ref an FOM or anything else that specifies a STart Up, Fuel FLow LIMITATION?


User currently offlineApathoid From , joined Dec 1969, posts, RR:
Reply 23, posted (12 years 3 months 3 weeks 4 days 15 hours ago) and read 4798 times:

Maintenance engine run check list for a CV-580 calls out for FF normal prior to the light off call. Only one I can think of off the top of my head, but I shall look if that is all you will believe. Why are you so opposed to the idea? Can you honestly say it is not the first warning you are going to have that it may be a hot start?

User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 24, posted (12 years 3 months 3 weeks 4 days 15 hours ago) and read 4799 times:

Better yet...

Have ya started a jet (or any gas turbine) in the past 48hrs?

Not witnessed it, simulated it, read about it, or watched it...but actually risked turning it into a "pile of slag" yourself? If so, please describe - engine type, fuel flows, egts, OAT, location. What about your last hot start?


25 EssentialPowr : What, exactly, is normal fuel flow for a Convair 580 on a standard day at Dallas Love with an 850 hr engine? Otherwise reread what I wrote. Fuel flow
26 Apathoid : I frequently run Garrett TFE-731 and TPE-331 as well as some good ol' GE CJ 610's. Last start was about 9 am this morning (a 331.) I am also fully qua
27 EssentialPowr : Don't need to... But again, what is the max fuel flow limitation for any of those engines on start up?
28 Apathoid : You are making my argument for me. If fuel flow is abnormally high, the result COULD be a hot start. I never said that it was the primary indication,
29 EssentialPowr : You have current and contemporary experience with TPE 331s, PT6s or TFE 731s...and your first ref above was for a Convair 580?? That's rather strange.
30 Apathoid : You asked for a powerplant that reference fuel flow on the engine start checklist. The CV-580 is the only one I can think of off the top of my head.
31 EssentialPowr : FF can't be primary b/c there is NO defined LIMITATION; that's why it is defined as "Normal". FF as a secondary, yes. Not primary; for the 5th time no
32 EssentialPowr : OK - So, AGAIN, what's a normal startup ff for a CV580 (STD day, Dallas LUV, 850 hrs)????
33 Apathoid : That is EXACTLY what I said you rube. I said it was the FIRST indication of an abnormal start. I did not say abort the start because of it. Geesh. You
34 EssentialPowr : Easy now. Rube is HARSH! So, what is an abnormal fuel flow? If you can't define normal (for ANY of the powerplants you listed), how do you know what a
35 EssentialPowr : "You run engines your way and I'll runthem my way, which by the way is the way our AOMs, MMs & training manuals tell us to run them." I couldn't agree
36 Metwrench : My turbine engine experience for Maintenance run-up's: RR Dart, fuel flow is extremely critical, a secondary "trimmer" is used during start to control
37 Air2gxs : Last engine run: about 2 hours ago N527UP B747-200 JT9D-7Q KSDF Power run for trim due to throttle stagger gripe. All 4 engines. OAT 54 F EGT max star
38 JETPILOT : "Impending hot start" is on the FAA's list of things to do when certifying a crewmwmber. If you dont catch a high fuel flow and make the call out... "
39 EssentialPowr : Wrong. The FAA doesn't write or define engine start procedures for ANY airline; the FAA only approves them. As a result, they leave the airlines to de
40 EssentialPowr : "Maybe you mis-understand. Every high initial FF does not result in a hot start. Its just the 1st indication you get that tells you that you MAY have
41 Post contains images FDXmech : There is no defined hard limititation on fuel flow because high FF in itself, does not constitute a parameter affecting the structural integrity of th
42 EssentialPowr : Did I ask anyone to define what a hot start was? No way. I didn't agree with the 4th post. FF is not a primary, or first indication of a hot start sim
43 727pfe : If we would just accept the fact the each airline operates in it's own fashion, maybe we would stop having discussions with dozens of conflicting post
44 EssentialPowr : Bingo. A hard limit; so I would now concur that FF is a primary parameter for 727 pfe's airline. Thanks for the example. The point is; until a discret
45 FDXmech : EP You're exasperating, to say the least.
46 Apathoid : Okay, here ya go...from the manufacturers recommended operation procedures, NOT airline policy: GE CJ610 Turbojet Operation Instructions Normal Proced
47 EssentialPowr : So why couldn't you cite that parameter earlier? That's kind of "basic" isn't it? Quote it, and you've made your point as 727pfe did, and note, I acce
48 Apathoid : Um, you aren't worth talking to. I gave you the answer you wanted and you are still being nothing but an argumentative prick. You slashed everyone her
49 Air2gxs : Apathoid: Ditto for me.
50 L-188 : EssentialPowr: You do realize that some people don't bring home the company maintaince and flight manuals at the end of the day. They do have lives. D
51 Notar : HELICOPTER When you start a turbine engine it is very susceptible to heat damage especially in the combustion chamber (burner can) since it is not gen
52 VC-10 : I thought this discussion was dead after the first couple of post's. I come back after a few days and it's still goimg ! One has to accept Flt Dk engi
53 EssentialPowr : Apathoid (and Air2gxs) ***Please reference exactly where I stated that "fuel flow is NOT an important parameter to monitor during light off"?**** I sa
54 EssentialPowr : ***Please reference exactly where I stated that "fuel flow is NOT an important parameter to monitor during light off"?**** Still waiting... Due to you
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