FLCH Takeoffs
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From: nowhere
FLCH Takeoffs
We seem to always takeoff with VNAV armed but we did train in the sim for normal takeoffs without VNAV and then at an appropriate altitude, a selection of FLCH and selection of a target climb speed. Then a press of a button to reduce thrust to climb.
Has anybody had need to do this on the line.
Has anybody had need to do this on the line.
Last edited by JammedStab; 13th October 2013 at 06:26.
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From: UK
Hi JammedStab,
For the first 26 years we flew aircraft which were not permitted to use flight directors for take off and didn't have a VNAV function anyway.
B737-200 was operated the way you describe.
Has anybody had need to do this on the line.
B737-200 was operated the way you describe.
Thread Starter
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From: nowhere
But what reason could there be for doing this on the line unless you were to have some concern about the validity of VNAV. I believe that this results in not having FD guidance for engine failure scenarios encountered below the acceleration height.
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From: EU
We never used VNAV on T.O. Boeing say you should consider not using VNAV if the weathers a bit dodgy, relating to windshear. There are also some software issues in the FMC which somehow relates to VNAV and windshear. This isn't the full story, but it's something along these lines.
Last edited by pudoc; 13th October 2013 at 16:00.
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From: Seattle
Also a useful procedure if your contingency procedure states an early turn with V2 and you want to accelerate and clean up after turn is completed
In our 774/748 fleet we ALWAYS use TOGA with VNAV armed for takeoff. I can remember only 2 instances in 10 years on the 744 when TOGA failed to engage and I had to place the thrust levers manually.
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From: Out of radar space
Never done it before. I once had to handle the levers manually as TO mode did not start. Or maybe inop all before the flight, still didn't read anything in the documentation. There was no need to cancel the take off when you still have hands to push throttles and keep N1 stable. But never FLCH, never heard or used before.
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Answer discovered later...
Limitation on LNAV/VNAV with QFE is that any conditional altitudes in the FMS are referenced to QNH, not QFE. Secondary (Minor) consideration is airplane without GPS and doing DME updates will get slant angle/range wrong using QFE. In reality, if the departure doesn't have conditional waypoints, and the plane has GPS, VNAV will work without any issues for the very short time you are below the transition altitude.
FMC does not know altimeter is on QFE, so a conditional alt is with a condition, like after reaching 4000' turn left, where you can't manually code the point in yourself. Something like 5000B at a specific point you could actually could make work, as you could adjust the altitude and change it 4000B, (assuming 1000' field elevation using QFE)
For LNAV, the NAV accuracy for non-GPS planes is degraded by the slant range error.
In reality, most planes have GPS, or the slant range is not going to make a big enough error to really make a difference in LNAV unless you really need a low RNP.
Last edited by JammedStab; 24th December 2013 at 19:57.
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From: Seat 1A
Originally Posted by Clarrie
The question was
Quote:
Has anybody had need to do this on the line.
not has any one done this on the line!
Quote:
Has anybody had need to do this on the line.
not has any one done this on the line!
Joined: May 2000
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From: Seattle
Intruder.......who is pushing any buttons here? If in VNAV that would be the case though in this scenario.
By contrast, if you armed LNAV and VNAV and used TOGA for takeoff, all you have to do is open the speed window after the speed bug jumps from V2 to initial climb speed. Autothrust and Flight Director takes care of the rest.
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From: dunnunda
In the venerable Douglas/Boeing 717 ✈️ as flown by Bloggs, the system is a little different if using Level Change.
At or above 500' AAL, the PM selects AUTOFLIGHT & LEVEL CHANGE (pulls the level knob). This engages the autopilot and changes auto throttle from TAKEOFF. CLAMP, to TAKEOFF THRUST, which then allows the auto throttle to select climb power at the appropriate point. The aircraft is climbing at V2.
At ACCEL, the PF pulls the speed knob, initiating acceleration from V2 to enroute climb.
At or above 500' AAL, the PM selects AUTOFLIGHT & LEVEL CHANGE (pulls the level knob). This engages the autopilot and changes auto throttle from TAKEOFF. CLAMP, to TAKEOFF THRUST, which then allows the auto throttle to select climb power at the appropriate point. The aircraft is climbing at V2.
At ACCEL, the PF pulls the speed knob, initiating acceleration from V2 to enroute climb.
