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B737 - anyone use the MCP N1 and SPEED buttons

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B737 - anyone use the MCP N1 and SPEED buttons

Old 8th Mar 2021, 21:17
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B737 - anyone use the MCP N1 and SPEED buttons

B737 - anyone use the MCP N1 and SPEED buttons?

Those are two buttons that never seem to be used.

If so, when and under what scenarios.
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Old 9th Mar 2021, 04:44
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From B737 theory.

A/T speed modes are:
FMC SPD using the FMC target speed
MCP SPD using the MCP selected speed
Automatic A/T speed mode selects when the DFCS is engaged to either FMC SPD or MCP SPD depending on the active pitch mode.
Manual A/T speed mode selection is accomplished by pushing the SPEED button on the MCP.
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Old 9th Mar 2021, 05:03
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In normal operation on a modern 737, never.

N1 was used on every takeoff on old 737s, which didn't have selectable automatic thrust reduction, to select climb thrust at 1500 ft (or where desired).

SPEED can be used to switch A/T into ARM mode, where only certain protections will be active, but thrust is manually controlled by the pilot. Popular with some airlines/pilots to use it on approach in order to be able to use A/T in case of go-around, but Boeing FCTM recommends against using this technique.
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Old 9th Mar 2021, 09:59
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erjdriver1

It depends on the variant of 737. On an NG; seldom used. Some carriers permit the use of the SPEED button to allow manual thrust on approach, with the A/T armed for use during a go-aroundn but Boeing doesn't recommend it. I seem to remember BAW/GOE being advocates of the 'speed off' method.
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Old 9th Mar 2021, 11:03
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Yes, when I flew the classic about 20 years ago we also deselected speed on approach when hand flying. Why does Boeing not recommend this practice?

As was stated before, I'm pretty sure we pressed N1 at acceleration altitude on departure to command climb thrust.
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Old 9th Mar 2021, 11:40
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Originally Posted by 733driver View Post
Why does Boeing not recommend this practice?
Possibility of inadvertent A/T alpha floor function activation during flare, which would increase risk of tailstrike or long landing.
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Old 9th Mar 2021, 11:59
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Thanks. Never seen this happen and don't recall if the low speed protection is still armed in the flare. Would have to check the manual. Also, we only operated the -300 so at least the risk of a tail strike would have been minimal but a long landing would have been a possiblity if the A/T did indeed add thrust in the flare
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Old 9th Mar 2021, 12:22
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but a long landing would have been a possiblity if the A/T did indeed add thrust in the flare
There are still pilots that give a burst of power as they flare in the mistaken belief it makes for a smoother touch down. Once a pilot is addicted to this technique it is hard to eradicate. (like smoking)

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Old 9th Mar 2021, 12:40
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733driver

If it activates it goes directly into retard mode below 27 ft RA (as proven by Turkish Airlines). Pretty much a non-issue.
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Old 9th Mar 2021, 14:02
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Thanks Denti from a former colleague
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Old 9th Mar 2021, 20:12
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How about pressing speed to engage speed mode? (Like after an RA or GPWS event)
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Old 10th Mar 2021, 14:00
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If there is any AFDS pitch mode active, A/T will automatically engage in SPD/N1/ARM mode after it's armed following a disconnect.
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Old 11th Mar 2021, 10:53
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I have a vague memory that the SPD button can be pressed while in ALT ACQ mode while the A/T mode is FMC SPD, if it is desired to alter the speed during ALT ACQ.

This was really only relevant on the classics, as the NG has a SPD INTV button also which achieves the same purpose, although this button may have been a customer option on early NG’s.

Having said that, in my entire career, I have never pressed it.

The SPD button may have had a more important purpose on the pre-classic models.
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Old 18th Mar 2021, 20:52
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in my company we use N1 button at acceleration height to engage the AT into climb thrust
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Old 18th Mar 2021, 21:39
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Of what vintage is your FMC software?

Automatic thrust reduction has been available for at least 20 years now.
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