spacemantan,
Re. a four engine aircraft, Vmca2 is not a consideration for a four or three engine GA, and the aircraft limitations section of the AFM will include details of the demonstrated height loss in a GA. It is measured in tens of feet, not hundreds.
Only when you get to Cat II/III is there a potential for a touchdown during a GA, in any event, you never retract the U/C until you have a positive rate of climb.
Generally, certification does not allow for double failures (as in a second engine failure on a three engine GA in a four engine aircraft) the potential number of "double failures" is just too great.
For a B744, for example, there is no adjustment to any minima for an (1) engine out approach, compared to all engines. This is the AFM, individual NAA/airlines may impose more restrictive condition than as certified.
Further, in the event of a double engine failure, you do not commit to an approach until you know you can complete the approach, and have a landing clearance.
A good rule of thumb is "Gear down, go down" ---- from that point you are committed to a landing. You do not plan on a two engine GA on a four engine aircraft, even if, under favorable circumstances, it might be theoretically possible.
Again using the B744 as an example (and typical of FAR 25 aircraft), something called Vmco does not figure, the typical T/O climb speed to the initial cleanup altitude will be V2 + 10kt (+10 to + 25 does not significantly alter the rate/angle of climb) and for a GA, V2 is minimum, more typically V2 + 5, again to the initial cleanup altitude ---- which may be 400', but more typically 800', unless obstacles dictate a higher altitude.
Tootle pip!!
Last edited by LeadSled; 17th April 2010 at 04:44.