View Full Version : Mode C verification
fireflybob
25th Sep 2016, 20:52
From a pilot can someone from ATC please confirm the tolerances for verification of mode C?
Cleared For A Coffee
25th Sep 2016, 21:08
From a pilot can someone from ATC please confirm the tolerances for verification of mode C?
Tolerance for verification of Mode C is +/- 200ft
fireflybob
25th Sep 2016, 21:33
Tolerance for verification of Mode C is +/- 200ft
Many thanks
whowhenwhy
26th Sep 2016, 20:52
At the risk of sounding like a pedant, it's worth pointing out that the +/- 200 ft does not reflect the pilot's (+/-100 ft) or aircraft's (differs based on date of manufacture) altitude keeping ability and only reflects the effects of altimetry and surveillance system errors. I say this only because I've heard some pilots discuss their belief that +/- 200 ft for SSR Mode C verification equates to their 'wriggle room' around a cleared level.
From ICAO doc 4444, as it may apply this way for other countries...
8.5.5.1 VERIFICATION OF LEVEL INFORMATION
8.5.5.1.1 The tolerance value used to determine that pressure-altitude-derived level information displayed to the controller is accurate shall be ±60 m (±200 ft) in RVSM airspace. In other airspace, it shall be ±90 m (±300 ft), except that the appropriate ATS authority may specify a smaller criterion, but not less than ±60 m (±200 ft), if this is found to be more practical. Geometric height information shall not be used for separation.