b-747 questions!

[lamjura]

Can nay one answer the ff?
1. Is there a critical engine in 747 ? if yes then which one and what makes it a critical engine ?

2. What is tandem bogie ?

3. If you take off 747 IFR minimum and experience an engine failure after some time, do you come back an land or continue to destination ?

Thanks !

lamjura



------------------
look & you shall see....
listen & you shall hear..
seek & you shall find....

[john_tullamarine]

the answers are not particular to the 747

(a) the concept of a critical engine in propeller aircraft relates to the change in direction of airflow through the prop disc and the resulting lateral movement of the net thrust line for each motor at takeoff pitch attitudes due to prop blade angles on the rising and falling blade side of the disc .. the motor which has the thrust line move outboard gives the greater yaw moment ... hence failure of the other motor (with inboard thrust line movement) causes the maximum control difficulties .. the latter motor is then referred to as the critical one because its failure causes the most control difficulty. With a jet, the engine is ducted from an airflow viewpoint .. so there will not be any movement of the thrust line ... and there will be no critical engine in a fashion similar to propeller aircraft.

Another problem relates to the normal (vertical) force associated with this airflow direction change .. and the similar force at the front of the jet engine .. but that is tied up with pitch stability rather than yawing problems.

(b) refers to the undercarriage assembly geometry on large aircraft .. multiple axle assemblies eg two axles on most larger main gear units.. and on some, even more . eg the 727-ski has a 3 axle main and 2 axle nose

(c) post failure planning depends on the crew's assessment of

(i) urgency to land
(ii) weather minima
(iii) local terrain and actual weather
(iv) available letdowns
(v) crew familiarity with the airport

etc ...

this assessment will lead to a decision whether to

(i) return via a visual circuit
(ii) return via a letdown
(iii) divert to a more suitable alternate

[cpdude]

Can you say......Cathay interview?

[Bargearse]

Critical engine on a jet, as I understand it, is the upwind engine on any crosswind takeoff as you have limited, additional rudder to counter an engine failure. On a 747 it would be the outboard, upwind engine.

[john_tullamarine]

Not a common use of the term 'critical engine' in respect of crosswind handling considerations. It is usual to consider the certification meaning.

So far as the crosswind concern might be a worry, consider the following situation when it is a REAL worry. Try a min V1 takeoff, strong crosswind from the side with the V1 failure, and aft limiting CG ... it is called .. running off the side of the runway ..and is pretty well guaranteed.

Always gets the students' undivided attention when you give them the exercise in the sim on endorsement training and helps to keep the consideration in the back of their minds for line ops.

[Bargearse]

Sorry, I should have been clearer in my answer.

When you are asked what the critical engine for the 747 is in an interview, whether it be with Cathay or whoever, they are referring to the crosswind takeoff situation I mentioned.

Personnal experience.

Bargie.

[This message has been edited by Bargearse (edited 06 May 2001).]

[lamjura]

Hi Everyone!

Thank you very much for your answers.

Happy Landings.

Lamjura

[john_tullamarine]

just because it is asked .. doesn't make it any less wrong .... why ever not just ask the question in terms of which engine when failed causes the greatest handling difficulty in a crosswind takeoff ...? I am incredulous .. but, then again .... I have heard of some weird interview questions ....