B737 Loss of Thrust on Both Engines
Join Date: Apr 2010
Location: Home soon
Posts: 0
Likes: 0
Received 0 Likes
on
0 Posts
Strange, to me it implies that the actions of a relight are primary (hence recall items) to restart while the engine is already at high rpm regardless of aircraft altitude and airspeed (as stated in the FCTM quote).
Speed setting being secondary.
If speed were so important for a relight then it would have been positionned at the beginning of the memory part of the checklist.
Therefore i still doubt boeing expects crews to go into an overspeed to achieve that speed and still vote for B
Also the inflight relight,windmill enveloppe speed is shown to be at a minimum of 140 kts and maximum of 340 kts ..would it mean something?.
Speed setting being secondary.
If speed were so important for a relight then it would have been positionned at the beginning of the memory part of the checklist.
Therefore i still doubt boeing expects crews to go into an overspeed to achieve that speed and still vote for B
Also the inflight relight,windmill enveloppe speed is shown to be at a minimum of 140 kts and maximum of 340 kts ..would it mean something?.
Last edited by de facto; 8th Mar 2014 at 19:41.
Thread Starter
Loss of Thrust on Both Engines
Dual engine failure is a situation that demands prompt action regardless of altitude or airspeed. Accomplish memory items and establish the appropriate airspeed to immediately attempt a windmill restart.
Dual engine failure is a situation that demands prompt action regardless of altitude or airspeed. Accomplish memory items and establish the appropriate airspeed to immediately attempt a windmill restart.
The first sentence tells you take prompt action. What action? The second sentence tells you: Complete the Memory Items and establish the appropriate airspeed.
Keep the high RPM you have in the engine and try to relight as soon as possible - just as you said. Also, keep the high RPM by getting to a higher airspeed.
One pilot is running the restart, the other is pitching for the airspeed.
Also the inflight relight,windmill enveloppe speed is shown to be at a minimum of 140 kts and maximum of 340 kts ..would it mean something?.
FCTM:
The in-flight start envelope defines the region where windmill starts were
demonstrated during certification. It should be noted that this envelope does not
define the only areas where a windmill start may be successful.
demonstrated during certification. It should be noted that this envelope does not
define the only areas where a windmill start may be successful.
The engine cares about burner pressure in order to relight. What Boeing has to say is about how to achieve this burner pressure in an altitude vs airspeed mode..
You can have lots of pressure at low altitude but unless you can get this to the combustor it aint gonna light. You can have lots of airspeed at high altitudes but the total pressure at the burner may be too low to stay lit.
As you can guess you need some help from the spinning engine to convert some of the speed to pressure. This balance is what defines the inflight restart envelop.
Yes you may be lucky and get it started outside this envelop but if you cook the turbine in a bad start it's all over. Not to mention it seriously impacts your ability to hang around in a proper restart envelop. Too many accidents have this in their causal chain
You can have lots of pressure at low altitude but unless you can get this to the combustor it aint gonna light. You can have lots of airspeed at high altitudes but the total pressure at the burner may be too low to stay lit.
As you can guess you need some help from the spinning engine to convert some of the speed to pressure. This balance is what defines the inflight restart envelop.
Yes you may be lucky and get it started outside this envelop but if you cook the turbine in a bad start it's all over. Not to mention it seriously impacts your ability to hang around in a proper restart envelop. Too many accidents have this in their causal chain
Get a working flight director in level change
It should be remembered that if the thrust levers are in cruise setting when the dual engine flameouts occur you do not close them as part of the attempt at initial re-start. See QRH.
Join Date: May 2001
Location: A few degrees South
Posts: 809
Likes: 0
Received 0 Likes
on
0 Posts
Judd.
Level change has nothing to do with closed trust levers. It simply opens now your speed window, and the FD shows you how to fly present speed between the two speed limits.
As your VNAV will probably disconnect by itself upon loosing the two engines, the pitch mode will revert to ALT HOLD, showing you a stall in the making.
Of course you can do all this raw data, but the FD makes it easier, especially turning in a safe direction, and decending just enough to maintain safe speed.
Level change has nothing to do with closed trust levers. It simply opens now your speed window, and the FD shows you how to fly present speed between the two speed limits.
As your VNAV will probably disconnect by itself upon loosing the two engines, the pitch mode will revert to ALT HOLD, showing you a stall in the making.
Of course you can do all this raw data, but the FD makes it easier, especially turning in a safe direction, and decending just enough to maintain safe speed.
Join Date: Nov 2013
Location: Australia
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
My thought is that maybe Boeing wants you to keep the engines moving and forget about the MMO.
Why would you consider the compounding of a very bad situation with also overstressing the airframe. Please don't quote the " there are margins built into this.." crowd. You would find yourself with two engines shutdown, the overspeed clacker going off and the PFD looking very disconcerting by being into the red.
The inflight start envelope caps out at 24000ft. If your goal is to get to 275 to maximise your chance of the restart then your argument is flawed because you are too high. If you want to maximise your chance of an inflight start you should do a emergency descent to 24000ft, set the speed to 281-340 and try there. There may be other reasons why you don't want to do that but yoru question does not expand on the exact scenario you are contemplating.
Join Date: Aug 2006
Location: wyoming
Posts: 252
Likes: 0
Received 0 Likes
on
0 Posts
Follow the QRH but do not overspeed the aircraft therefore answer B would be the logical choice. Most 737 simulators are programmed to not allow an engine to relight inflight unless the speed parameters are met. I routinely give this scenario in the sim as an Instructor but usually around FL 310. Many pilots attempt the QRH actions but they don't have 275 knots. The red line speed is mach .82 and about 290 knots at FL 310 depending upon simulator preprogrammed conditions. If the pilots do not get to 275 knots the engines will never relight. I actually had a crew dead stick it in to a vfr airport one time because they never achieved the required speed parameters ie 275 above FL270 and 300 knots below. They slowed to 250 knots at 10,000 feet so they never had a chance at low altitude as the sim won't allow you to relight unless you have the required parameters met. I debriefed them they had good pilotage gliding skills but poor checklist discipline.
Thread Starter
So it sounds like a lot of us think that "at or above FL270, set airspeed to 275 knots" means many things. So here's what I've distilled (forgive me if I generalize):
I like WYOMINGPILOT's story about not relighting because the pilots slowed to 250 below 10000. I just wonder if that staying below MMO is the same mistake.
- Cosmo Kramer - L/D Max or 275/MMO
- Lomapaseo - L/D Max
- Latetonite - within the amber limits
- Sudden Winds - "Doesn't Matter"
- John Farley - L/D Max
- De Facto - 275/MMO
- Travelling Gav - VMO/MMO until you're in the certified envelope
- WYOMINGPILOT - 275/MMO
- ImbracableCrunk - 275
I like WYOMINGPILOT's story about not relighting because the pilots slowed to 250 below 10000. I just wonder if that staying below MMO is the same mistake.
Join Date: Jan 2008
Location: farmm intersection, our ranch
Age: 58
Posts: 206
Likes: 0
Received 0 Likes
on
0 Posts
I vote for coming into the start envelope with the most energy and thus ability to stay in the start envelope the longest. Accelerating at lower altitudes makes the earth get larger at an alarming rate.
Remember, you get 30 minutes if battery plus one APU start attempt. Again, why waste more of your battery life waiting to get into the APU start envelope.
Remember, you get 30 minutes if battery plus one APU start attempt. Again, why waste more of your battery life waiting to get into the APU start envelope.
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
Likes: 0
Received 0 Likes
on
0 Posts
It seems to me that people here confuse "Loss Of Thrust On Both Engines" with "Engine In-Flight Start".
In case of "Engine In-Flight Start", only one engine has failed, and you have tons of time to either start the engine that had a flameout or prepare for a one engine inoperative landing..
In the case of "Loss Of Thrust On Both Engines", the point is to get an immediate relight on at least one of the engines, by following the QRH memory items. The rest of the checklist is for a dire emergency and, as I see it, does not necessarily provide a successful outcome.
If the engines doesn't immediately relight, the chance is that they won't - most likely due to a fuel problem (ran out or contaminated). I think the most important thing is to get the start switch set to flight, and to cycle the start levers. If e.g. the dual flameout is cause by high altitude icing.
Give me one other good example why both engines would otherwise fail simultaneously...
In case of "Engine In-Flight Start", only one engine has failed, and you have tons of time to either start the engine that had a flameout or prepare for a one engine inoperative landing..
In the case of "Loss Of Thrust On Both Engines", the point is to get an immediate relight on at least one of the engines, by following the QRH memory items. The rest of the checklist is for a dire emergency and, as I see it, does not necessarily provide a successful outcome.
If the engines doesn't immediately relight, the chance is that they won't - most likely due to a fuel problem (ran out or contaminated). I think the most important thing is to get the start switch set to flight, and to cycle the start levers. If e.g. the dual flameout is cause by high altitude icing.
Give me one other good example why both engines would otherwise fail simultaneously...
Thread Starter
Cosmo Kramer, I've wondered about how often this checklist has been or will be used. Maybe older engines that were less tolerant of upset, ice, etc. required this and is now a holdover from certification.
The question would be academic if it wasn't a something we're required to be able to demo or perform.
The question would be academic if it wasn't a something we're required to be able to demo or perform.
Last edited by ImbracableCrunk; 10th Mar 2014 at 21:48. Reason: Englishy
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
Likes: 0
Received 0 Likes
on
0 Posts
Not once have I done this in the sim. It's a bs exersice anyway, in my humble opinion (guess I had luck with sensible companies/instructors). What is there to learn from doing it in the sim? Except to learn how the sim was programmed. Memory items? You can practice those with your eyes closed, you don't need to waste costly sim time on that. There are no handling issue to learn, as you just have an aircraft descending.
Then rather use the time to learn how to dead stick it, and from low altitude, like severe damage on both engines after takeoff with two close airports. But this is not a requirement anyway...
Then rather use the time to learn how to dead stick it, and from low altitude, like severe damage on both engines after takeoff with two close airports. But this is not a requirement anyway...
