Critical Engine on the 747?

[Clowndown]

Is there a critical engine on the 747 and if so...which one...and why? Thank you

[Snot Box]

Handling the Big Jets will give you the answer. :)

[Clowndown]

I really don't want to have to purchase a whole book to find out one answer. I have been using a lot of my old college books but none of them seem to have any 747 stuff in them.

[gissmonkey]

are you studying for interview? If so, being too cheap to buy a great book is a good reflection of your enthusiasm;)

[18-Wheeler]

No.
Though Vmcg & Vmca are quite different with one or two engines out on the same side.

[Traffic]

..unless of course you happened to be taxiing a Saudi 743 in Aug01 with just #2 & #3 alight...and knew nothing about the hydraulic system...in which case I would say that #1 would be critical.....but that's just being pedantic.

[fire wall]

Clowndown, the correct answer that they are looking for is that which is the into wind engine on the takeoff role. Simply explained as a xwind from the left will apply a yawing moment to the left with all engines running.....lose # 1 and the yawing moment is compounded. Conversely lose # 4 and the yawing moment is not as great.

Good luck

[HardRock]

Upwind, outboard on four engine aircraft.

[Medwin]

Nope, its the downwind outboard.

[FOUR REDS]

To be absolutely correct:

It depends on whether the aircraft has positive or negative weathercock stability......

On the 4-engined jet I fly, which has POSITIVE Weathercock, the AFM states that the Critical Engine is the OUTER Engine on the UPWIND side.:confused:

[catchup]

@four reds

Yes, that's how understand the forces.

regards

[Paracab]

One would hope that in the two years that have lapsed since this thread began that Clowndown may have discovered the answer....

[FOUR REDS]

It's obviously still topical for some people, including you!!!!!

[Paracab]

FOUR REDS,

Purely tongue in cheek old chap. Never noticed this thread before.

Pc

[FOUR REDS]

Paracab, understood. Thanks:ok:

[john_tullamarine]

This topic (and quite a few similar) regularly arises on PPRuNe. Suggest that a search on "critical engine", "Vmcg", and "Vmc" (or "Vmca") will give you more than a coffee's worth of reading.

Certification things of interest are

(a) directional control characteristics
(b) loss of systems

while the typical interview question tends to relate to the crosswind consideration (which, basically, is ignored at certification). The thing to keep in mind here is that Vmcg is determined for nil wind (7 kt under the UK requirements) ... if you happen to be in a critical takeoff situation, with a decent crosswind ... then don't have an engine failure.

[GlueBall]

Traffic: ...Brakes are available without motors No. 1 & 4 turning; it would require only rudimentary systems knowledge. :eek:

[pictues01]

Also had the Saudi crew crossfed the power to the proper HYD Systems they wouldn't have had the problem either.

[mutt]

Saudi crew

What Saudi crew? There wasnt ANY flightcrew in the cockpit.

Mutt.

[Tinstaafl]

Surely he meant 'crew' in the sense of 'the people crewing the aircraft'? After all, 'flightcrew' wasn't used.

[fire wall]

Mr pictures,
"crossfed the power to the proper HYD Systems"
to clarify:
I was informed by a KL stationed gnd engineer that the a/c was taxiing after maintenance with only engines 2 and 3 operating......engineers at the controls. Unfortunately normal brakes operate from hyd sys 4 and alternate from sys 1. Bringing the ADP on line on either system would have averted the embarrasment or flicking up the reserve brake switch which runs off hyd sys 2 (with operating EDP and maybe ADP if the brought such on line).........switch with big flashing RED brake source light located near Capt R knee.

I operated into KL the next day and the gnd engineer took me to the a/c. No security about so got withing 20 metres ...... the visual aspect to the external damage was incredible and I understand the internal damage to structure just as so. First class area (seats 1-10 or there abouts) floor pushed up towards roof of lower cabin.

Anyway, back to topic. There still seems to be some confusion re the topic of critical eng. I have quite a bit of time on type and can assure those that it is the upwind engine. I beleive the Q comes from a tech exam run for first joiners to a "swoosh" airline based in Asia (now that one cannot be too difficult to work out). Raised eyebrows will be accompanied by the answer of downwind donk!

[Semaphore Sam]

Which is 'the' critical engine? The one(s) still turning, regardless of crosswind. Others are dead weight; fly what you have.