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As per definition the Minimum Vectoring Altitude (MVA)

in each sector provides 1000 ft above the highest obstruction [...].

I am curious where these 1000 ft stem from. Why not 500 ft? Why not 300 ft, or 600?

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SKYBrary that you've quoted usually cites ICAO. In this case, ICAO makes no mention of the 1,000 ft, only the temperature corrections to apply (by the pilot*) in PANS OPS.

*

There is little in ICAO Documents defining who is responsible for terrain and obstacle clearance. Existing references are contradictory, or do not reflect the modern ATM environment, with direct tracking, vectoring and RNP procedures regularly taking aircraft off published ATS Routes.

— International Federation of Air Traffic Controllers' Associations - 54th Annual Conference – Sofia, 20th to 24th April 2015 (PDF)

But 1,000 ft serves its purposes:

  1. Provides enough reaction time for the controller to notice a pilot deviation and take action while allowing enough time to recover, e.g. a misheard or incorrectly entered altitude
  2. Would not cause EGPWS alerts: going lower than the runway field clearance floor will sound the TOO LOW TERRAIN alarm – the proposed 300, 500, and 600 ft are either too close to or below the floor depending on how far out the plane is; similarly for other obstacle clearance warning systems in light planes
  3. Provides good enough buffer for when the temperature is too cold if left uncorrected for by the pilot.

enter image description here
EGPWS runway field clearance floor (RFCF) from Airbus flight manual

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    $\begingroup$ The ATC standard IFR vertical separation (radar or non-radar) between aircraft is also 1000 feet. The ATC vertical separation between aircraft or between an aircraft and terrain were likely developed from the same early safety analysis. And, this separation standard (minimum vectoring altitude) has stood the test of time. Probably difficult to ever identify the original source and data that were used in coming up with 1000 feet. $\endgroup$
    – 757toga
    Nov 17 '21 at 21:29

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