B757 VNAV manoeuvre margin

[EPRman]

I have always understood that with VNAV engaged the manoeuvre capability is 1.6g to max.lift coefficient at .80M for CAA aeroplanes and 1.3 for FAA aeroplanes.But when selecting the MAINT page of the FMC on our CAA aeroplanes the manoeuvre margin reads 1.3.This is the same whether it's on the non-PIP or Pegasus FMC's.Asking around the answers vary.One is that VNAV ensures 1.6 regardless of what the box says,another is that it should read 1.6 and you can select 1.6 in the scratch pad and change it but it's an engineer's job.Most of the time people just shrug their shoulders!As this has implications regarding what the FMC tells you regarding climb and cruise capability I was wondering what the definitive answer is.Any suggestions?

[ 17 October 2001: Message edited by: EPRman ]

[Checkboard]

On the 733, the FMS alllows the operator to select the manoeuvre margin between 1.1, 1.2 & 1.3 for operations in the U.S. but in Australia it was fixed at 1.3

[QAVION]

"I have always understood that with VNAV engaged the manoeuvre capability is 1.6g to max.lift coefficient at .80M for CAA aeroplanes and 1.3 for FAA aeroplanes.But when selecting the MAINT page of the FMC on our CAA aeroplanes the manoeuvre margin reads 1.3."

Are these values (1.6 and 1.3) 757-specific? On the 747-400, for example, it's 1.2 for FAA regs and 1.3 for CAA (British and Australian) regs.

Note that for some aircraft, updating the monthly Nav Database can result in the Maintenance Page figures resetting to default values(e.g. 1.2 for Manoeuvre Margin for the 747-400). It's up to Maintenance to ensure that the correct value is in there for your particular airline after software updates have been carried out. This value should not be adjusted by the pilot under normal circumstances.

BTW, doesn't your airline have a software sheet say, in the Tech Log, which tells you what your values should be? If it is supposed to be 1.6 on your aircraft, I'd be asking Maintenance about it.

Rgds.
Q.

[av8er]

During conversion to Pegasus I noticed a customer option to select the 'Manoeuvre Margin' within the range 1.3 to 1.6G (757/767).

However, the definition of 'Manouvre Margin' is not clear and I have heard discussions of either Max lift coefficient or to initial buffet. Not sure what the answer is - any clues?

[Gypsy]

Manoeuvre margin can be selected through Perf Factors (but you need to know the little codeword to effect a change).

CAA requires 1.3g and FAA 1.2g as the limits.

Optimum level gives you about 1.5g (44 degrees AOB) except on short flights when it will give you the level at which you can get to achieve the minimum cruise time which is also specified in the Perf factors (usually 1 min).

[PPRuNe Towers]

Dunno whether it is related to an incident, legal advice or some plain old CYA but the FAA now 'allow' 1.3 to be chosen for the margin rather than 1.2.

However - 1.2 is still a legal margin for use.

Regards
Rob