Engine failure during cruise

[ElNull]

If an engine failure occurs at cruise altitude, it may be necessary to descend. The autothrottle should be disconnected and the thrust manually set to CON. On the FMC CRZ page select the ENG OUT prompt, followed by the prompt corresponding to the failed engine. This displays the engine out cruise data and the FMC calculates engine out target speed and maximum engine out altitude at the current gross weight. The fields are updated as fuel is burned. Do not execute the page if VNAV is required for any arrival procedures. If any ENG OUT page is executed then FMC will not transition to descent.

Set the maximum altitude in the MCP altitude window and the engine out target airspeed in the MCP IAS window. Allow airspeed to slow to engine out speed then engage LVL CHG. If the "Engine Out Target Airspeed" and "Maximum Continuous Thrust" are maintained, the airplane levels off above the original MAX altitude. However the updated MAX altitude is displayed on the ENG OUT CRZ page. After viewing the engine out data, select the ERASE prompt to return to the active cruise page.

After level off at the target altitude, maintain MCT and allow the airplane to accelerate to the single engine long range cruise speed. Maintain this speed with manual thrust adjustment. Entering the new cruise altitude and airspeed on the ECON CRZ page updates the ETAs and TOD predictions.

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the above is from the 737 flight crew training manual.

From what I understand is, first I should disengage Autothrottle then select MCT from the FMC and then adjust thrust manually to MCT rating.

but how can I allow the airspeed to decrease to the driftdown speed while in level flight and thrust at MCT? (isnt it necessary to maintain MCT while descending?)

[kharmael]

Because you'll have one less engine providing thrust?

[Nimer767]

the comment above is true ,

you will not have the same amount of thrust , Since you are cursing at high altitude means you need more power to increase the speed at level flight , when you are haveing a single engine the speed might be constant or decrease even with MCT , Its a Single Engine !

[Lord Spandex Masher]

Flight sim...............hopefully:ugh:

[Northbeach]

ElNull,

You remember from your studies that in unaccelerated steady flight, constant airspeed, thrust equals drag.

If your Boeing 737 NG is flying at cruise altitude and your airspeed is stable at a given mach, say .78, the thrust of your engines equal the drag generated by your airplane. Now if one of your two engines fails; and you do nothing but maintain altitude, very quickly the airspeed will begin to slow (decay).

The airspeed will slow because you have 50% of the thrust you had before the engine failure, all the drag you previously had plus you have added the drag created by the inoperative engine wind milling in the air. Your thrust was reduced by 50% and your drag increased significantly. Your airspeed will decay. If you do nothing but try to maintain altitude with pitch, you will stall.

Disconnecting the autothrottles keeps them from moving with virtually every small environmental change and minor airspeed fluctuation. The procedures will have you set maximum thrust on the operating engine. Allow the airspeed to slow to the most efficient airspeed {maintain the altitude you have as long as you safely can to give you the most range} given the circumstances (target speed, driftdown speed). Your Boeing’s FMC will give you target speed and optimal altitude for conditions. You have maximum continuous power on the one remaining engine and you will descend at the “optimal speed” down to the “optimal altitude” as long as you need to stay at cruise.

While maintaining MCT on the operating engine and flying the optimized driftdown speed you will not over speed the aircraft provided you do not lose control of the aircraft’s pitch and stay on, or very close to, your target driftdown airspeed. At normal cruise weights and altitudes setting MCT on the only operating engine will not suddenly accelerate the aircraft past VNE/MMO/whatever your high speed limit happens to be. It is not like smashing down the accelerator on your sports car and keeping the accelerator pinned to the floorboards while driving on the autobahn/highway/freeway.

You are to be commended for asking the question and trying to understand the “procedures” rather than simply accomplishing them by rote. I am no longer surprised by such questions. You are not the only one.

I know of an ex-military trained crew (Think BIG western country that prides itself on being the “best”. However the following could have happened to a civilian trained crew as well.) The “incident crew” was flying a civilian two engine airliner. This crew experienced exactly what you described a simple engine failure at cruise. That (military and civilian trained crew) experienced crew (two of them) did not descend (unbelievable-underlying terrain was NOT a factor). They stayed at altitude until they got the stick shaker (warning to an impending stall). Fortunately, after getting into the stick shaker, they descended (rather than falling out of the sky).

The only bad question is the one you do not ask. Remember for your own sake and on behalf of tens of thousands of people who will entrust their lives into your care, and the myriads of their relatives and loved ones; as a professional pilot, concerning your chosen profession, what you do not know, do not understand, or lack the necessary skills to do has the potential to hurt/kill/ruin your career every time put on the uniform and go flying. Let that thought sink in!

Ignorance is not bliss! Virtually any given flight can go from routine to incredibly demanding and stressful in an extraordinarily short amount of time.

Do you have any more questions?

Respectfully, and at your service (as are most of us here on PPRuNe)

Northbeach

[411A]

The autothrottle should be disconnected and the thrust manually set to CON.

Clearly this is a poor quality FMS installation.

From very long ago, on the first jet airliner to be equipped with a full authority dual FMS...
Engine failure in cruise.
Select engine inop/driftdown page.
Select critical or non-critical.
Press execute.

That's it, from an airplane operational perspective, the FMS does it all for you (except call ATC and ask for that lower altitude).
Since 1977.
Type...Lockheed L1011.

Absolutely no need to 'disconnect' anything.
All VNAV normal functions are preserved.

TriStar...far far ahead of everyone else.
And, apparently with some new(er) types...still is.;)

[galaxy flyer]

Not sure about Boeing, but Honeywell FMS on GLEX procedure is set manual speed to drift down target speed, set MCT, select FLCH, await descent at drift down IAS until level off. The autopilot will hold altitude until slowing to drift down IAS, then descend.

GF

[ElNull]

thank you all that was really helpful

Northbeach thanks for explaining, but talking about thrust and drag.. thrust decreases with height and therefore the the drag might exceed available thrust (near the maximum altitude). isnt this why the maneuver margin decreases and the amber bands (min and max maneuver speeds) becomes narrower?

[Northbeach]

ElNull,

I just got home from another trip and started typing out an answer, but decided to go in a different direction ask you some questions instead with the ultimate purpose of coming to an understanding regarding the questions you posed in post #8.

Your information says that you are from Egypt, so I am going to assume I am talking to a young Arab airline pilot. The questions I ask are not a “test” nor am I in a position to “teach” you anything, nor I am not trying to trap you in some mistake. Rather my purpose is to stimulate a discussion that will perhaps further my own understanding of such matters; one professional aviator to another (and whoever else may chime in or lurk).



Thrust decreases with height


Why does thrust in your General Electric CFM-56 engine decrease with height?


isn’t this why the maneuver margin decreases and the amber bands (min and max maneuver speeds) become narrower?


What exactly are those amber bands on the airspeed indicator, and what are they telling you?

If your aircraft were in perfectly still air and you were flying at an indicated airspeed of 250 knots at 12,000' and we compared that first aircraft's ground speed to a second jet exactly the same as the first jet in every way also flying at 250 knots indicated airspeed but at FL410. Both aircraft are over the same spot flying in the same airmass with zero wind at altitude and both flying the exact same indicated airspeed of 250 (KIAS). What would be the relationship between their two ground speeds? Both are indicating 250 KIAS in still air at exactly the same weight the only difference being altitude; the first jet at 12,000 MSL, the second jet at 41,000 MSL are their ground speeds the same, is one jet faster over the ground than the other?

[de facto]

Your information says that you are from Egypt, so I am going to assume I am talking to a young Arab airline pilot. The questions I ask are not a “test” nor am I in a position to “teach” you anything

What does being from Egypt have anything to do with TAS?

If your aircraft were in perfectly still air and you were flying at an indicated airspeed of 250 knots at 12,000' and we compared that first aircraft's ground speed to a second jet exactly the same as the first jet in every way also flying at 250 knots indicated airspeed but at FL410

Im lost already :sad:

[ElNull]

Why does thrust in your General Electric CFM-56 engine decrease with height?

- because the air density decreases with height (the air entering the engine will have low density and that decreases the thrust)

What exactly are those amber bands on the airspeed indicator, and what are they telling you?

- they are the minimum and maximum maneuver speeds. If we are flying at speeds below the minimum maneuver speed or above maximum maneuver speed, the maneuver margin and loadfactor decreases (i.e the aircraft might stall at smaller bank). speeds between the amber bands provides adequate maneuver margin (or atleast 0.3 '40 bank') as FCTM says. also 'flap maneuvering speeds' are the recommended speeds that provides full maneuvering capability.


- to answer your last question, the higher jet will be faster because at the constant 250 KIAS, TAS increases with height.

[Nimer767]

Enull did you get the answer for your first question ?

[ElNull]

Yes, thanks for your concern, Nimer767!

[Northbeach]

defacto,

TAS has no relationship on being a young Egyptian Arab pilot.

However, the amount of respect, deference, word choice and posture I take will vary depending on whom I am trying to communicate with. In trying to communicate effectively with a young Arab professional pilot I would make the extra effort to be much more respectful than I would to a Westerner.

Northbeach

[Northbeach]

ElNull,

You are exactly correct in your answers.

You know at the higher altitudes the air is much less dense, therefore the engines have less mass to accelerate and turn into thrust. Your CFM 56s are still capable of providing max N1, but there just isn’t enough mass in the atmosphere to provide the same thrust the engine can provide at sea level.

For the same reason the wing passing through that rarified air (at FL410) is unable to generate the same amount of lift at the slower speeds the same wing was able to at the lower altitudes.

At FL180 we have about half the density we have at sea level.

So, you are accurate again:

the drag might exceed available thrust (near the maximum altitude).

If you are at cruise at FL410 with two engines and then lose one the airspeed will decay. Even if you go to MCT on the one remaining engine, depending on weight and temperature, it will most likely not be able to provide enough thrust to keep you out of the low speed buffet range. This is what happened to the crew I sited that tried to stay at altitude following the loss of one of their two engines; their airspeed decayed and the aircraft experienced the stick shaker before the crew descended.

So in many ways you are correct here as well:


isnt this why the maneuver margin decreases and the amber bands (min and max maneuver speeds) becomes narrower.


The higher you fly the less mass there is in the atmosphere to support the weight of your aircraft. The narrowing amber bands become a visual clue of the acceptable range of operation. You demonstrated understanding of the difference between two airplanes both indicating 250 KIAS but at vastly different altitudes. It is the application of that understanding that answers your question as to why the maneuver margin decrease as the aircraft flies higher in the atmosphere. See, you already knew the answer! Well done.

Respectfully,

Northbeach

[Nimer767]

you welcome mate . ESHTA ;)

[Nimer767]

And Northbeach thank you for the info's above that was helpful for everyone .

[ElNull]

thanks Northbeach, really appreciated!