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PCTool
26th Mar 2008, 18:38
Hi all. Am I correct in thinking that Minimum Flap Retraction Altitude and Acceleration Altitude are the same thing ie: the altitude that acceleration is commenced (by lowering the pitch Attitude) and retracting flaps on schedule?
Or is Acceleration Altitude to do with being on a single engine climb to what is usually 800 ft AAL and then level acceleration to flap retraction speeds as distinct from MFRA?
Also, V2+15 is the target climb speed and provides a certain bank angle protection. Can someone provide some more information on this?
Many thanks.

TolTol
26th Mar 2008, 23:17
Minimum Flap Retraction Altitude is the altitude at which you accelerate and clean up after an engine failure. e.g. 1000'agl.

Acceleration altitude is the altitude at which you accelerate and clean up after a normal take-off, e.g. 3000'agl.

411A
27th Mar 2008, 02:39
Minimum Flap Retraction Altitude is the altitude at which you accelerate and clean up after an engine failure. e.g. 1000'agl.

Acceleration altitude is the altitude at which you accelerate and clean up after a normal take-off, e.g. 3000'agl.

Somewhat close, but no cigar.

If we look back in time, we find that the MFRA is a certification standard, from CAR4b, and on piston, turbopropeller and early jet transports, was/is 400 feet AGL...or, more correctly, the runway surface elevation.

However, certain airfields with obstructions off the end of the runway, have a higher MFRA, dependant on the elevation of the obstacle.
In certain cases, a turn to avoid the obstruction can result in a lower MFRA, however in no case can it be lower than 400 feet AGL -or- that altitude specified during certification of the aircraft, as demonstrated by the manufacturer.

Now, looking at normal operating practices used by airlines, the normal flap retraction altitude can be an altitude dependant on the preference of the airline -or- that altitude required by noise abatement procedures for the particular airfield.

As can be seen in the second situation, like many things in commercial aviation...it depends on several variables.

PCTool
30th Mar 2008, 20:09
Toltol and 411A, many thanks for the information. It makes more sense now..:ok:

Empty Cruise
31st Mar 2008, 04:39
...and minimum MFRA remains 400 ft for all JAR/FAR-25-types. However, many manufacturers state a "general" MFRA that can be used for training purposes etc. (where no limiting obstacles exist, of course), and many pick 1000 ft AAL.

However, any given departure will have a minimum MFRA that will either be 2nd segment limited or 400 ft. as per certification - and a maximum MFRA, where the drag of the config will compromise the enroute portion of the SE climb. You rarely run into this 2nd restriction (unless you are used to alpine operations) - but it's still there, theoretically.

The 1000 ft. is just chosen to give the average student a bit more time and to allow time for any recall items to be actioned before accelerating.

The acceleration altitude is often based on NAPs and will thus often be 1500 ft or 3000 ft AAL.

john_tullamarine
31st Mar 2008, 05:24
where the drag of the config will compromise the enroute portion of the SE climb

OEI more commonly limited by max time at T/O thrust (or, occasionally, something more obscure .. eg the Dart is limited by max time for the feather pump to run)

Chris Scott
31st Mar 2008, 13:19
Quote from PCTool:
Also, V2+15 is the target climb speed and provides a certain bank angle protection. Can someone provide some more information on this?
[Unquote]

My knowledge is very limited, and am unable to access any manuals, so have been hoping someone would enlighten us on the above; possibly a Boeing driver?

If memory serves, bank angle in the initial climb (prior to flap-retraction) was a big issue on the B707 (-320). At V2, it was limited to 15 degrees. To enable 30 degrees, you needed V2+15. So any close-in turns to avoid obstacles had to take that into account for the engine-out case, where it was not possible to accelerate to V2+15. [In the all-engine case, the initial climb speed was always V2+15.]

As far as I can remember, all the other jet types I flew (including the VC10) permitted 30 degrees of bank at V2. Presumably, it is bound up in the relationship between the certificated V2 and Vs. Does the B707 offer less "fat" because of its age (since initial type-certification) or was this (and, perhaps, is this still) a Boeing thing?

As for the situation after clean-up, figures of V2+45 and V2+60 may have allowed banks of 15 degrees and 30 degrees respectively on the B707?

Could B727/737/747/756/777 pilots please bring us up to date?


Just one other point on flap retraction, for all multi-engine types: is it fair to specify that it is normally conducted in a gentle climb in the all-engine case; but in level flight in the engine-out case?

fogatgatwick
31st Mar 2008, 14:19
on a 737 3-900 one uses 15 degrees max bank when below V2 + 15 or Vref15 + 15 on a Go Around

single engine cleanup after take off is 400' minimum or as specified in the emergency turn procedure. Also cleanup occurs in level flight (i.e not turning) only. company SOP is to use a higher height as a minimum. Cleanup would be in level flight or a gentle climb depending on how much excess thrust is available

to cleanup after a go around single engine, one recalls that the missed approach obstacle area doesn't include a level segment, so if one is unable to make one's own terrain assesment, then one would maintain the flap setting until the go-around stop level, or some other suitable height

point8six
31st Mar 2008, 18:02
B747 -all variants, max. bank angle 15 degrees at V2 - V2+10 kts.
Min flap retraction 400' agl, unless otherwise stated for airfield.

point8six
31st Mar 2008, 18:05
Where possible, flap retraction for B747 'Classics' is level flight, following engine shutdown; however, for B747-400, flap retraction is during (reduced performance) climb.

411A
1st Apr 2008, 02:39
Does the B707 offer less "fat" because of its age (since initial type-certification) or was this (and, perhaps, is this still) a Boeing thing?



Turns with takeoff flaps selected.

Early models of the B707-300 series airplanes required V2+15 for thirty degrees of bank because they did not have full-span leading edge devices (except those aircraft which were originally delivered new to South African Airways)

However, later fan-powered varients did have full span LED's, so the minimum speed for a thirty degree bank was/is V2+10.