737-400 Low Idle Light
Thread Starter
Join Date: Aug 2003
Location: GREECE
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
737-400 Low Idle Light
On my return trip to our homebase this morning i got a "LOW IDLE" light indication along with the MASTER CAUTION "ENG" indication.
We carried out the checklist that states for the A/T to be disengaged and the THRUST LEVERS to be advanced until the light is out.
Problem was that the same aircraft would be used by us on a second flight so we flipped the MEL but the only answer we could find was for the "LOW IDLE lt ".
Discussing the problem with the company engineers they suggested to do a static run up with the A/G sensor CB in and out and compare the engine idle values.
This was done the problem disappeared and we went on our next flight.
My question is...are there any restrictions concerning the "LOW IDLE" system because when i referenced the books i couldn't find any !!
Thanks !
We carried out the checklist that states for the A/T to be disengaged and the THRUST LEVERS to be advanced until the light is out.
Problem was that the same aircraft would be used by us on a second flight so we flipped the MEL but the only answer we could find was for the "LOW IDLE lt ".
Discussing the problem with the company engineers they suggested to do a static run up with the A/G sensor CB in and out and compare the engine idle values.
This was done the problem disappeared and we went on our next flight.
My question is...are there any restrictions concerning the "LOW IDLE" system because when i referenced the books i couldn't find any !!
Thanks !
Join Date: Dec 2000
Location: on the golf course (Covid permitting)
Posts: 2,131
Likes: 0
Received 0 Likes
on
0 Posts
Turbineblade
My recollection from several years ago is that the low idle condition is brought about by the system sensing that Flight Idle is not achieved and the system is still in ground idle - several % N1 lower than flight idle. Flight idle allows the engines to spool up much quicker for power/speed demands when on approach primarily. As such, while it is desirable, by disconnecting the A/thr and manually advancing the thrust levers to the flight idle setting, you will still have the (manual) quick spool up required in flight, so the flight is ok to proceed. As I say this is from 737 recollection and by logic - which could be fallable.
Rgds
My recollection from several years ago is that the low idle condition is brought about by the system sensing that Flight Idle is not achieved and the system is still in ground idle - several % N1 lower than flight idle. Flight idle allows the engines to spool up much quicker for power/speed demands when on approach primarily. As such, while it is desirable, by disconnecting the A/thr and manually advancing the thrust levers to the flight idle setting, you will still have the (manual) quick spool up required in flight, so the flight is ok to proceed. As I say this is from 737 recollection and by logic - which could be fallable.
Rgds
Join Date: May 2003
Location: The Roman Empire
Posts: 831
Likes: 0
Received 0 Likes
on
0 Posts
Blade, after you applied the non normal cklist, did you have a chance of trying, after a few minutes, if retarding one thrust lever to idle the light illuminated again?
Did you have the ignition switch on FLT when it happened?
Anyway, your question is a good one: we are not given enough information on how to behave in such a case, for the next flight.
Academically, the captain should report in the tech logbook the malfunction at the end of the flight, so a new crew could take the airplane only after maintenance have checked the problem and answered.
The procedure they suggested is good, the one they would have used if they had to respond on the book.
Next question: if the light came back during the runup, would you have flown the airplane again?
Captain's decision, I'm afraid...
Did you have the ignition switch on FLT when it happened?
Anyway, your question is a good one: we are not given enough information on how to behave in such a case, for the next flight.
Academically, the captain should report in the tech logbook the malfunction at the end of the flight, so a new crew could take the airplane only after maintenance have checked the problem and answered.
The procedure they suggested is good, the one they would have used if they had to respond on the book.
Next question: if the light came back during the runup, would you have flown the airplane again?
Captain's decision, I'm afraid...
Join Date: Jan 2001
Location: Sweden
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
Hi Blade,
It has been a few years since I last worked on the B737, I seem to remember that the low Idle light illuminates under the followinging conditions.
* Inflight
* Eng A/I on
* Any Eng N1 less than 45%
The reason behind this light (It was an Airwothiness Directive) was a series of flameouts early on in the CFM56-3īs service life. This AD also dictated shortening the HP/LP splitter lib in the engine, as well as replacing the conical shaped spinner with a bullit shaped one.
So If I had been your freindly groung engineer this morning, and if i had no spares to do it with(I wouldnīt have
) I would have adviced you to monitor your engine parameters closely in icing condition, and adviced you to keep your N1 above 45% at all time.
Brgds
Doc
It has been a few years since I last worked on the B737, I seem to remember that the low Idle light illuminates under the followinging conditions.
* Inflight
* Eng A/I on
* Any Eng N1 less than 45%
The reason behind this light (It was an Airwothiness Directive) was a series of flameouts early on in the CFM56-3īs service life. This AD also dictated shortening the HP/LP splitter lib in the engine, as well as replacing the conical shaped spinner with a bullit shaped one.
So If I had been your freindly groung engineer this morning, and if i had no spares to do it with(I wouldnīt have
) I would have adviced you to monitor your engine parameters closely in icing condition, and adviced you to keep your N1 above 45% at all time.Brgds
Doc
Thread Starter
Join Date: Aug 2003
Location: GREECE
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
LEM...the start switches were on the "CONT" position at the time the light came on.We advanced the thrust levers several times and the light went out.However when the T/L's were pulled back to idle the light went on again.
On your second question the answer in NO...i wouldn't fly the machine if the problem was there after the run up.
DOC..the fellow engineer on board suggested the same thing that the conditions for the light on are the ones you mentioned.
However i had a disagreement with him(not that i doubt the engineers) because the books for the 737 mention that the engines have 2 idle speeds (22% on Ground and 32% in FLT) and whenever the idle speed of the engine goes below 32% in flight the light comes on.So it was pretty clear for me !
My question is..." are there any operational restrictions when this light comes on"...The MEL is not of any help !
The method for the run up was pretty simple....started both engines and then the engineer pulled the A/G switch CB !
On your second question the answer in NO...i wouldn't fly the machine if the problem was there after the run up.
DOC..the fellow engineer on board suggested the same thing that the conditions for the light on are the ones you mentioned.
However i had a disagreement with him(not that i doubt the engineers) because the books for the 737 mention that the engines have 2 idle speeds (22% on Ground and 32% in FLT) and whenever the idle speed of the engine goes below 32% in flight the light comes on.So it was pretty clear for me !
My question is..." are there any operational restrictions when this light comes on"...The MEL is not of any help !
The method for the run up was pretty simple....started both engines and then the engineer pulled the A/G switch CB !
TurbineBlade
Doc had it about right, however I would add that the safety concern is associated with penetration of a storm front ala the Easyjet thread above.
It isn't so much freezing weather as it is the ingestion of mixed precipitation in a severe storm front (mixed rain and hail).
In order to keep the engines running stable you need all the improvements he cites.
oops I forgot about low flight idle affecting fan blade icing on approach. Not a biggie but the increase in vibration tend to bother some pilots and Feds
However, as always the Boeing FCOM should supercede any free advice that you get on this forum
Doc had it about right, however I would add that the safety concern is associated with penetration of a storm front ala the Easyjet thread above.
It isn't so much freezing weather as it is the ingestion of mixed precipitation in a severe storm front (mixed rain and hail).
In order to keep the engines running stable you need all the improvements he cites.
oops I forgot about low flight idle affecting fan blade icing on approach. Not a biggie but the increase in vibration tend to bother some pilots and Feds
However, as always the Boeing FCOM should supercede any free advice that you get on this forum
Last edited by lomapaseo; 18th Aug 2003 at 07:14.
Join Date: May 2003
Location: The Roman Empire
Posts: 831
Likes: 0
Received 0 Likes
on
0 Posts
Just to clarify, mates, low idle is 21.5%, but HIGH IDLE has no fixed values, the average is 32% in flight, reducing at slower speeds and colder temperatures.
The conditions for the light are: below 25% N1, or below 45% N1 with ignition on FLT (as installed on the autothrottle) above 500ft radioaltitude.
Engine antiice is not a factor.
The conditions for the light are: below 25% N1, or below 45% N1 with ignition on FLT (as installed on the autothrottle) above 500ft radioaltitude.
Engine antiice is not a factor.
Thread Starter
Join Date: Aug 2003
Location: GREECE
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
LEM...thanks for the info...
I still wonder why Boeing Co. made those manuals look like magazines.Information is greatly reduced in comparison with the older manuals we had for the 737-200 and the 727 !!
Regards
I still wonder why Boeing Co. made those manuals look like magazines.Information is greatly reduced in comparison with the older manuals we had for the 737-200 and the 727 !!
Regards
Join Date: Jan 2002
Location: beyond PNR .. as always
Posts: 160
Likes: 0
Received 0 Likes
on
0 Posts
LOW IDLE LT.
Turbinblade, you didn't specify the flight phase. My 734 gave me the light (steady) at CLB thrust (?) , N1 well above 45% ! Engine anti-ice wasn't in use.
Hope DoctorA300 can help.
Thanks.
Hope DoctorA300 can help.
Thanks.
