B737 engine inop. GRADIENT with GEAR DOWN
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Joined: May 2003
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From: The Roman Empire
B737 engine inop. GRADIENT with GEAR DOWN
As you all know, the N2 tacho-generator is required on engine 1 for the proper operation of the LANDING GEAR TRANSFER VALVE.
This is a no go in the MEL.
In case of left engine failure, the landing gear would not retract fast enough to guarantee the minimum gradient at takeoff.
Talking to an instructor some time ago, he said in the AFM there's a table for engine out gradient with gear down...
I couldn't find it.
Maybe the page was missing, but I doubt it.
Do you have it?
LEM
This is a no go in the MEL.
In case of left engine failure, the landing gear would not retract fast enough to guarantee the minimum gradient at takeoff.
Talking to an instructor some time ago, he said in the AFM there's a table for engine out gradient with gear down...
I couldn't find it.
Maybe the page was missing, but I doubt it.
Do you have it?
LEM
Joined: Oct 2005
Posts: 264
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From: in them thar hills
Gear down ferry should be somewhere at the back of the AFM or DDG.
The section that has various corrections and penalties for bits missing etc. Sorry, I can't remember the name but CDL (configuration deviation limits?)comes to mind.
Most jet twins will fly OK at ferry weights with an engine out and the gear hanging out in the breeze. Most will not, and are not required to, fly at high commercial weights with BOTH an engine failure AND the gear stuck down. Because many certification requirements do not assume multiple failures, i.e both an engine quits at V1 and the gear won't come up. You may as well say both engines might quit therefore all airplanes have to have at least three engines and be capable of flying away from V1 on only one of the three.
On the other hand, if you do get to do a gear down ferry, you do have to hold the weight back to some pretty low value and probably the AFM will call for increased V1 just in case one engine fails, as that is the 1st (and only) assumed failure on that particular flight. En route performance and fuel also has to be adjusted.
But if a tacho fails on an ordinary flight and you can't get the gear up, you've had your one failure on that trip, as far as the law is concerned. Common sense says you would not dispatch if you discovered it before takeoff (or maybe before 80 knots if that is your SOP) and if it happened late in the takeoff or after takeoff you'd return for a landing, if possible "just in case". But if the departure airport wasn't suitable for a return you could still go somewhere else without breaking the law, even if performance was compromised and even if you gobbled up your fuel reserves.
This exercise makes an interesting LOFT and I am sure it has been done to death in the simulator. However, to subsequently introduce an engine failure at a point where the airplane can not arrive somewhere under full control is unreasonable. Multiple and simultaneous or near-simultaneous failures are sometimes taken too far by some simulator instructors who can spook ordinary god-fearing line pilots with unrealistic scenarios.
The section that has various corrections and penalties for bits missing etc. Sorry, I can't remember the name but CDL (configuration deviation limits?)comes to mind.
Most jet twins will fly OK at ferry weights with an engine out and the gear hanging out in the breeze. Most will not, and are not required to, fly at high commercial weights with BOTH an engine failure AND the gear stuck down. Because many certification requirements do not assume multiple failures, i.e both an engine quits at V1 and the gear won't come up. You may as well say both engines might quit therefore all airplanes have to have at least three engines and be capable of flying away from V1 on only one of the three.
On the other hand, if you do get to do a gear down ferry, you do have to hold the weight back to some pretty low value and probably the AFM will call for increased V1 just in case one engine fails, as that is the 1st (and only) assumed failure on that particular flight. En route performance and fuel also has to be adjusted.
But if a tacho fails on an ordinary flight and you can't get the gear up, you've had your one failure on that trip, as far as the law is concerned. Common sense says you would not dispatch if you discovered it before takeoff (or maybe before 80 knots if that is your SOP) and if it happened late in the takeoff or after takeoff you'd return for a landing, if possible "just in case". But if the departure airport wasn't suitable for a return you could still go somewhere else without breaking the law, even if performance was compromised and even if you gobbled up your fuel reserves.
This exercise makes an interesting LOFT and I am sure it has been done to death in the simulator. However, to subsequently introduce an engine failure at a point where the airplane can not arrive somewhere under full control is unreasonable. Multiple and simultaneous or near-simultaneous failures are sometimes taken too far by some simulator instructors who can spook ordinary god-fearing line pilots with unrealistic scenarios.
Joined: Aug 2001
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From: Europe-the sunshine side
The eng 1 N2 tachometer indicator may be inoperative but the N2 tachometer generator for eng1 must be operational for dispatch.
The fact that the N2 tachometer generator is operational can be verified by checking the AVM analyzer for coresponding fault code (not a pilot job) or by checking at start that engine start switch automatically move to off.
After that it's no way to check if it fails.
If the tachometer generator works it will send the signal that the engine failed,and the gear will be raised by the LGTU at a NORMAL rate. The hydraulic liquid used to raise the gear (from sys B ) will be lost.
The fact that the N2 tachometer generator is operational can be verified by checking the AVM analyzer for coresponding fault code (not a pilot job) or by checking at start that engine start switch automatically move to off.
After that it's no way to check if it fails.
If the tachometer generator works it will send the signal that the engine failed,and the gear will be raised by the LGTU at a NORMAL rate. The hydraulic liquid used to raise the gear (from sys B ) will be lost.
Joined: Jun 2004
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From: Australia
The information that you seek is available in the AFM, but not under the title that you may think.
Look at the 1st Segment Climb performance, all of that is predicated with the gear down, just apply that data to the 2nd segment for obstacle clearance etc. Not much use for 3rd, 4th, and subsequent phases of flight however.
Regards,
Old Smokey
Look at the 1st Segment Climb performance, all of that is predicated with the gear down, just apply that data to the 2nd segment for obstacle clearance etc. Not much use for 3rd, 4th, and subsequent phases of flight however.
Regards,
Old Smokey
Joined: Oct 2005
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From: in them thar hills
Good point old smokey - 1st segment would give you a feel for how it would go if the double-failure situation arose, i.e one quit at V1 plus the gear stayed down. But it would not be the basis for planning a ferry with the gear down, for as you say it is useless information at later phases of flight. I can't find it in any of my old and now very superseded manuals either. Next time I am anywhere near a real airplane I will try to find it in the AFM, but even then, different countries sometimes include different appendices with the AFM.
Thread Starter
Joined: May 2003
Posts: 831
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From: The Roman Empire
Excellent point Old Smokey as usual!
It should be there, but I couldn't find it
As we have a fleet of airplanes coming from every corner of the world, I'll try to find it again in the next days to come.
In the meanwhile, if somebody finds it for the 737 classic, let's say a 55 tons sea level ISA+10, it's most welcome!
Thank you, LEM
It should be there, but I couldn't find it
As we have a fleet of airplanes coming from every corner of the world, I'll try to find it again in the next days to come.
In the meanwhile, if somebody finds it for the 737 classic, let's say a 55 tons sea level ISA+10, it's most welcome!
Thank you, LEM
