Outboard engine failure

[18hazelwood]

Hello all,

Just some questions if someone could help,

Been practicing some engine outages...

Say engine N0 4 is out in flight (Cruise), would rudder trim alone be the only necessary step to keep operational level flight?

What speed can safely be achieved on 3 engines in the cruise?

Between slower and faster speeds with say N0 4 engine out, would different rudder inputs be necessary to keep level flight? i.e. transiting from say 250knots down to 180knots - less to more input on the rudder)?

Might be obvious to most, but I would appreciate any guidance on how to do things properly.

Many thanks in advance, your help is appreciated.
18 hazelwood.

[Jeroen Hoppenbrouwers]

Your FMC will tell you the target one-engine-out speed for your weight etc.

You certainly will need to descend. You cannot maintain altitude with less than four engines. But it is not going to be a brisk maneuver. Your speed will start to reduce slowly with all remaining engines on max continuous, and then when it hits the FMC-calculated engine out speed, you need to start trading altitude. This is called "drift-down". Sometimes you are assigned a block altitude by ATC so you can actually drift down at that speed. Often you need to just go down to the next level you're cleared to, which typically is a tad below your maximum altitude with engine out. Your FMC also calculates this altitude for you. In such a case, use the normal FL/CH system. I don't know whether V/S is recommended -- usually V/S drops some protection somewhere so I can imagine you don't want it if you are already known underpowered and more critical. You certainly don't want to descend at 100 ft/min too little and slowly bleed off under your target speed.

When your speed decreases, you need more physical rudder deflection to correct for the yaw. However the 744 has a rudder ratio changer so probably you do not need to adjust a lot, if anything.


Hoppie

[18hazelwood]

Many thanks Hoppie,

I really appreciate your guidance, it is much appreciated ...

I will now practice some more ...

18hazelwood.

[Hardy Heinlin]

The rudder ratio changers adjust the ratio between pedal deflection and rudder surface deflection automatically when the airspeed varies, so you can keep your pedal deflection constant as long as your thrust is constant. Only when the thrust changes (not the airspeed) you need to change your pedal deflection (or trim). The trim moves the pedals.

Tip: In PSX, when you hit the brake pedals in flight (USB brake pedal button or spacebar on keyboard), your PNF will adjust the rudder trim until the slip indicator is centered. Just hit it once and watch the effect. When your thrust changes, hit it again.


|-|ardy

[18hazelwood]

Hello Hardy,

Many thanks for the info and the PSX tip, I will be trying this out for sure on my next flight ...

18hazelwood.

[andmiz]

All of Hoppie's advice is pretty good.

VNAV is the recommended descent mode in a drift down.  FLCH is also suggested as an option, but most of the literature points to VNAV.  However, in increasingly busy airspace we find ourselves in, the option for a slow drift down through multiple flight levels might just not be possible, and using FLCH with thrust at idle instead of VNAV with thrust at CON might be more advantageous. 

A descent may or may not be necessary.  It depends on your weight/altitude/temperature.  The speed achievable with an engine out also depends on those factors.  The FMC will give you two speeds, EO LRC which will be relatively fast compared to EO SPD, which is designed to allow a speed to wash off and maintain your initial flight level before a drift down descent. 

In practicality, I'd recommend you just follow the guidance from the FMC. 

[United744]

What I do is kick out the AT system, set CON thrust manually, and wait for the E/O speed.

I then start a manual 500 ft/min descent rate in VS mode. If the aircraft gains speed, then I just pull the thrust back slightly. If it is still losing speed, I hit FL CH.

500 ft/min is the required minimum descent rate through RVSM airspace for aircraft not RVSM capable. It also makes sure TCAS on *other* aircraft will see your descent rate and produce TAs for you. If you're too slow descending, TCAS can miss you, thinking you're not a threat.

E/O drift downs are fun!

Try Oceanic procedures for off-track descent and divert. These are even more fun!!

Over mountainous terrain, you have "escape routes" to consider. There are special charts showing areas that if you're in a specific area, where to go and minimum altitude you can descend to in that region.

[Britjet]

TCAS will never "miss" you. If you have a shallow descent rate it will react as though you were in level flight. A TA and possibly an RA will occur in the normal way.
Peter