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Part of the Concorde's aircraft limitations, from this answer:

le limitations of le Concorde

The last line of the given excerpt, and the one that this section concerns, reads:

Nose and/or visor operation must not be made below 500 ft above the terrain.

Why this particular limitation?

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    $\begingroup$ Perhaps to give pilots some room to get used to the different sight picture, including any optical distortions? $\endgroup$ Commented Apr 2, 2023 at 5:50
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    $\begingroup$ It would also violate “stabilized approach” criteria. And for what reason? Below 500’ you ought to be in takeoff or landing configuration and not monkeying with major changes to the airplane. $\endgroup$ Commented Apr 2, 2023 at 14:49
  • $\begingroup$ @MichaelHall: That sounds like answer material! $\endgroup$
    – Vikki
    Commented Apr 2, 2023 at 23:01

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I can’t speak with any authority on Concorde specific requirements, but it seems that changing the nose droop angle would be a fairly major configuration change. Below roughly 500’ AGL aircraft are generally considered to be either in the take-off or landing phase of flight, and manufacturers and airline operators prohibit configuration changes at low altitude.

Take-off phase – Take-off power and best climb speed are used to get safely away from the ground. With the exception of retracting the landing gear, nothing else but basic pitch control is touched. (roll control and rudder as needed to remain wings level, but no turns initiated) Above some predetermined acceleration height, (may vary by airline SOP, but 500 AGL is a good approximation) the aircraft is gently nosed over to accelerate to flap retraction speed. Around that time when the flaps are up the power may also be reduced somewhat to climb power for engine life and/or noise abatement procedures, and the aircraft may turn on course as it transitions from takeoff to climb phase.

Landing Phase – Below 1000’ AGL the aircraft should be ready for landing as the crew prepares to transition from approach to landing phase. For compliance with Stabilized Approach criteria, this requires that the aircraft be configured for landing, (gear, flaps, etc.) with the “etc.” in this case presumably covering the nose droop. Below 500’ especially the crew needs to be focused on instrument approach minimums and transitioning their scan to the runway environment for landing. I don’t know what sort of aerodynamic changes the nose causes, but it just doesn't make sense from a best practice standpoint to make any sort of change down low on a fast moving jet that is probably 20 seconds or less from touching down.

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    $\begingroup$ Though I think your intent is correct, the actual statement is patently false: "manufacturers and airline operators prohibit configuration changes at low altitude." Gear and flap retraction both occur below 500 ft AGL routinely and procedurally. $\endgroup$ Commented Apr 5, 2023 at 11:56
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    $\begingroup$ @MarkJonesJr., FWIW, both operators I have been involved with set an accel height of 400’ AGL. I intentionally avoided declaring some universal limit by using the generic terms “roughly” and “low”, and furthermore added “may vary by airline SOP, but 500 AGL is a good approximation” The question itself is evidence of at least one Mfg setting a limit of 500’. (I also excepted ldg gear retraction.) If you have credible knowledge or evidence that airlines routinely retract flaps significantly lower than 400-500’ AGL then please offer it. Otherwise I stand by my loose, vague, generic claim. $\endgroup$ Commented Apr 5, 2023 at 15:17
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The moving visor provided a large horizontal line in the pilot's view that moved up or down. This attracted the pilot's attention and they tended to pitch the aircraft together with the movement of the visor - which was usually not desirable below 500ft.

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    $\begingroup$ Seems reasonable. Do you have a reference? $\endgroup$ Commented Apr 5, 2023 at 11:54
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    $\begingroup$ ISTR reading this as a caution in the handling part of the FCOM years ago, and as a handling pilot I noted it as something to watch out for. It wasn't actually a problem once I knew to look out for the effect. $\endgroup$
    – RAC
    Commented Apr 8, 2023 at 13:07

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