Flying with 2 eng out

[Hardy Heinlin]

Garry, you are a genius.

That's it!


Cheerio :-)

|-|ardy

[74pilot]

While we're at it ...

... at the expense of some drag created by the rudder itself (You don't get anything for free).

I know. And that leads me to question #3 that I had in mind for a very long time already:

Performance tables and FMC VNAV features provide data for 2 eng out situations. These data are used for symmetric as well as asymmetric eng out situations. Is the difference in drag so small that it can be neglected?

|-|

2 engines out, they always fail in the same side, hahaha! At least in the simulator. In real life, should you get into this highly unlikely event (yes, I know it did happen a few times), then one engine out each side just means you will be somewhat better off than in the tables. The same goes for one engine out, on a quad. In the sim, it is almost always number one or four that bangs, and if it takes the air driven pump out or the entire hyd system, then you have an secondary/alternate flap issue as well. But for one engine out on a quad, there is no option for either inboard or outboard engines failed. Always assuming it is the worst case scenario, should number two or three fail, then you are just better off. Mind you, once I tried it (in the sim, again), it was awkward as I am used to so much rudder for an engine failure. An inboard failed is not much rudder at all.

[74pilot]

Ball half width off center is pretty close in the simulator, again, for now I speak for the classic 747 but it is almost the same airframe as the -400.

For any aircraft you need to keep it flying straight, even the smallest twin piston. The rudder will be designed to be able to counter this. If you could not, the drag penalty would be too much to be able to keep it flying, and having more than one engine is no longer an advantage. Many a small twin has been downed on this, actually, as it is one of the most challenging scenarios. Just search the NTSB or think of A... what was her name, she died in a Twin piston accident flying from a small island in a twin piston towards a larger one, where a jet was waiting for her. They were overweight, lost an engine and flipped over, crashed and burned.

There might be a little bit of slip and skid in an engine out situation, but referring to your own train on tracks, then imagine the length of the fuselage, how the air runs down the side of it. Imagine a 200+ foot aircraft, offset 5 or even 10 degrees towards the relative wind, the frontal area, the parasite drag would explode. On some lighter aircraft, flying with opposite rudder and aileron ("crossing the controls") is used as speed brake if too high on a power-off landing for instance. In some aircraft doing this intentionally is prohibited.

As for the banking into the live engine(s), it counters the yaw as well, but too much bank will mean to much requirement for more lift. But the tilted lift vector (toward gravity), helps offset the yaw produced by an engine out situation in a multi engine aircraft.

If you still don't see it, try to search online, there are lots of free tutorials for pilots, explaining all this with vector diagrams and probably much better than I can.

[Hardy Heinlin]

OK, thanks.

So, I assume, with eng #1 and #2 out, a stabilized crab angle of 4 degrees should then be realistic. Not zero, not five, something in between.

And for eng #1 out, perhaps 1 to 2 degrees.

(When heavy and with max thrust.)


|-|

[Jeroen Hoppenbrouwers]

On some lighter aircraft, flying with opposite rudder and aileron ("crossing the controls") is used as speed brake if too high on a power-off landing for instance.

Gimli Glider.

[Peter Lang]

For landing gliders this "slip" is common use. Also for landing single engine planes without flaps, such as Piper J3 C or some aerobatic planes. In this case not only to increase drag, it is also for better visibility of the runway ahead of you.

For Cessnas e.g. it is prohibited to slip with extended flaps.

Peter

[Hardy Heinlin]

Another thought ...

According to various manuals, the track line on the PFD might not be the same thing as the track line on the ND. (In PS1, both tracks are IRU tracks.)

The manuals say:

On the PFD, the track line indicates the airplane track from the selected FMC (or selected IRU if FMC data are invalid).

On the ND, the track line indicates the current track resulting from current heading and winds.

This text is vague. It could be interpreted so that the PFD track indicates the track of the current LNAV leg! This would explain why it looks so static in that video. The ND track might always be the IRU track, taking winds and asymmetric thrust into account.

Just a hypothesis. (Probably a wrong hypothesis. Of course, the FMC monitors the position, too; therefore it also knows airplane track.)

|-|

[Will]

Nice reasoning, Garry, that's correct.  Asymmetric thrust will create a yaw towards the dead engines.  You can counteract that yaw with rudder, stepping on the pedals on the side with the live engines.  That cancels the yaw, but now the plane is crabbed, which will cause the wing carrying the dead engines to lift.  Apply aileron to cancel the resulting bank, and you're good to go.  Most planes end up with the ball hanging 1/2 width towards the good engines for straight and level flight.

Hardy, defer to the experts for the amount of slip and bank that is needed.  In my commuter airliner, we flew wings level (not 4 degrees of bank) with the ball half-a-width out.  Of course, our tail wasn't that far behind the cockpit, so the drag from the fuselage wasn't as impressive.  In practice, "step on the ball" and then use ailerons to stop the resulting heading change.

[Hardy Heinlin]

Apply aileron to cancel the resulting bank, and you're good to go.

When cruising with engine out, would you apply aileron trim, or would you let the autopilot hold the aileron out of neutral all the time?

|-|

[Will]

Well, our mighty J32s didn't have autopilots.  We'd trim, always, both rudder and aileron, for hands-off flight, even with a failed engine.  When landing was assured, the PNF would zero the rudder trim, otherwise we'd leave it in.

[Barry]

If the yaw is removed by use of the rudder trim and the ailerons are centre, then the track and heading will be the same in no wind conditions.  In wind conditions the FMC will correct the heading to maintain track - providing you are in LNav but in non auto-pilot operations the ahi steering needle will enable you to maintain a given track.

[Hardy Heinlin]

If the yaw is removed by use of the rudder trim and the ailerons are centre, then the track and heading will be the same in no wind conditions.

I'm impressed – and I just believe you :-) Meanwhile I can imagine that a cruising 744 with 2 eng out "must" behave like a train on rails, with the fuselage perpendicular to the air mass. On the other hand, if I simulate an eng out yaw by applying some aileron, similar to a LAND 3 flare in cross wind, and compensate this yaw using some rudder, then the heading and track will be unequal. To a certain degree, the side of the fuselage will hit the air mass, otherwise the cross wind will push her off the runway centerline. So she must be able to fly with such a side slip drag.

Anyway, can I assume that what you said is valid for any asymmetric eng out condition, even with just one outboard engine running (during descent)?

And I assume that if you say "the same" you mean a difference of zero degrees, not one or two, but really zero?

Thanks,

|-|ardy

[74pilot]

You can fly it uncoordinated, but you will be out of control. Lots of drag, autopilot cannot cope, as it tries to adjust the course with the ailerons, totally uncoordinated. You HAVE to kick the rudder to get it under control. Boeing recommends:

1. Stop the yaw with the rudder
2. Adjust the wings to wings level
3. Adjust the rudder again, until the yoke is level

Then, the skid indicator should be almost in the middle, just slightly pointing towards the GOOD engines. Also slight bank towards the GOOD engines. A go-around on two engines is practiced in the sim, I am doing one tomorrow actually, and also did one last week. As long as you know how to work the rudder, it is OK. But going around, you have to decide land or not at around 1500 feet (flaps 20, gear up), then continue on the glide slope with almost max thrust, until you get the speed back, retracting to flaps 1. When reaching Ref+60 and flaps one, then you start to lift the nose (to keep the speed).

If two engines are out on the same side, and you give max thrust at low speed, you can risk you need full rudder trim, full rudder AND 15 degrees of bank into the good engines. Until you pick up speed, and the rudder becomes more effective, then you can add the last thrust on the outboard engine, if you had not already.

Since thrust varies with altitude and temperature, you have the highest Vmca2 around sea level and below usually 25 degrees (flat rated engines, depends which model/make). Worst case for the 744 is around 160 knots (TEI), where as OEI Vmca speed is close to stall or even below. You should be the fly on the wall in a sim session involving TEI and you would see it all much more clearly I think!

[Hardy Heinlin]

Thanks for the tips.

By the way, does your airline still have that 60 feet GPWS callout?

Good luck with your -400 conversion!

|-|ardy

[Richard McDonald Woods]

Can anyone give URLs for decent e/o tutorials?
Cheers, Richard

[74pilot]

Thanks

It is all going quite well, but I am also putting quite an effort into it.

I never flew any aircraft with the 60 foot call. Was it in a 747 Classic or -400? To my knowledge (for what I know/remember), all our -400s - depending on what minima is set - will say

TWENTYFIVEHUNDRED
ONETHOUSAND
FIVE-HUNDRED (yes, that little break between five and hundred)
PLUS ONE HUNDRED
MINIMUMS
50
40
30
20
10

And hopefully it does not say 20 and 10 toooo quickly after each other  :shock:  auch!

I don't know how much the new Aerowinx is built using the old logic, but I have found a list of issues in PS1 that need to be looked into. I am running it in DOSBOX on my mac, and I am not sure it is because of this, or whether it is a PS1 issue.

It seems to make a sensible calculation of a VNAV profile for descent, but as soon as it starts descent, it comes up with drag required. Speedbrakes will not always be enough to keep the normal rate of descent. I have checked QNH is set correct and all. If I put in a headwind in the weather section (but not in the CDU forecast page), it helps it maintain the profile, but it is not supposed to be like this. It seems that especially around FL300, it goes way above profile. I can also use speed intervention and go 360 knots WITH speed brakes, and it will also keep on profile (but this is not the intention!). So I think the calculation of the profile is OK, but the flight model is not correct - as if it was running at a higher idle? At high levels, with speedbrakes UP, you should get close to 4500 feet pr minute, depending on weight and speed. Almost all way down, in idle, it should be quite close to 3 nm for each 1000', depending on weight. Closer to MLW you will descend more shallow, whilst a light aircraft goes down faster (at the same descent speed). So a lighter aircraft should start descent later, but I am sure you know that.

On the CDU, holding the CLR key should delete the whole line in one go, if you press/hold it for one second, not one character at a time.

There are some issues also with VNAV PATH, especially on an RNAV or other approach using the VNAV function.

The 747 is really stable. In PS1 (maybe it is my DOSBOX installation?) it seems quite unstable, and it banks left and right in a nervous way, as it seem to try to track LNAV or whatever selected. Hunting the track or not, the rate of change of bank is much too quick in PS1, as if the aircraft had a lot less inertia.

When I have more time I can give you more feedback, but right now I still have a growing TODO list that needs taking care of ...

[Hardy Heinlin]

The 60 call might have been a Kai Tak feature (as Qavion said) until 1998.

PS1's VNAV is sensitive indeed (it also ignores the speed reduction to 250kt above 10000ft), but if it deviates that much as you're describing, I assume it's a DOSBOX timing thing. If the system timing is not right, the vertical speeds will be wrong.

In PS1, the CLR key intentionally doesn't hold-clear-all.

LNAV tracking nervosity in PS1 is known.

Cheers,

|-|ardy

[Will]

Back on the old, old forum (now three iterations ago, pre-2004), the LNAV nervosity was referred to by none other than H.H. himself as "chicken farts."  I remember it as if it were yesterday.

[74pilot]

Btw, those calls I wrote was just from memory. I noticed today that it says PLUS HUNDRED and not ONE HUNDRED. But I guess you know a lot more about that than I do

[Qavion]

Here's just some of the options...



Note that the 500' callout is a "smart" callout. It activates during non-precision approaches only.