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Altimeter Setting Procedures
- Flight level. Standard pressure setting (1013 hPa) is set when flying by reference to flight levels above the transition altitude;
- Altitude. Regional or airfield pressure setting (QNH) is set when flying by reference to altitude above mean sea level below the transition level;
- Height. Altimeter pressure setting indicating height above airfield or touchdown (QFE) is set when approaching to land at airfield where this procedure is in use.
Failure to set the appropriate barometric sub-scale pressure setting may result in a significant deviation from the cleared altitude or Flight Level
Types of Altimeter Setting Error
- The pilot mishears the transmitted pressure setting and sets an incorrect figure.
- The pilot hears the transmitted pressure setting correctly but fails to set it or mis-sets it.
- The pilot fails to change the pressure setting at the appropriate point in a departure, climb, descent or approach.
- Failure to set the appropriate pressure setting can result in deviation from the cleared altitude or flight level leading to level bust, loss of separation from other traffic, and even collision with other aircraft or with the ground (CFIT).
- Loss of situational awareness due to failure to appreciate the significance of a pressure setting (especially QFE as opposed to QNH). This can result in incorrect appreciation of the closeness of the ground possibly leading to an unstabilised approach or collision with the ground (CFIT).
- A pilot fails to ensure that standard pressure is set when passing the transition altitude in the climb, and levels the aircraft at a flight level which differs from the cleared level by an amount dependent on the difference between the QNH and 1013 hPa.
- A pilot fails to set QNH when passing the transition level in the descent and levels the aircraft at an altitude which differs from the cleared altitude by an amount dependent on the difference between QNH and 1013 hPa.
- A pilot un-used to landing with QFE set, does not remember that the altimeter now indicates height above airfield elevation or touch-down zone.
- The existence of appropriate SOPs for the setting and cross-checking of altimeter sub scales and their strict observance is the only universal primary solution to eliminate incorrect altimeter setting.
- Use of the aircraft radio altimeter to monitor the aircraft proximity with the ground can help to improve situational awareness provided that the flight crew are generally familiar with the terrain over which they are flying;
- GPWS/TAWS provide a safety net against CFIT and, in the case of TAWS Class 'A' with its option of a simple terrain mapping display, it can also be used to directly improve routine situational awareness.
Accidents and Incidents
Events in which the incorrect altimeter pressure setting was either a cause or contributing factor in a Level Bust or CFIT/near CFIT:
- A321, en-route, Vienna Austria, 2003 (WX LB LOC) (On 26th May 2003, a British Midland A321 suffered severe damage from hail en route near Vienna.)
- A319/B733, En route, near Moutiers France, 2010 (LOS LB HF) (On 8 July 2010 an Easyjet Airbus A319 on which line training was being conducted mis-set a descent level despite correctly reading it back and, after subsequently failing to notice an ATC re-iteration of the same cleared level, continued descent to 1000 feet below it in day VMC and into conflict with crossing traffic at that level, a Boeing 737. The 737 received and actioned a TCAS RA ‘CLIMB’ and the A319, which received on a TCAS TA, was given an emergency turn by ATC. The recorded CPA was 2.2 nm and 125 feet.)
- B734 / MD81, en-route, Romford UK, 1996 (LB LOS HF) (On 12 November 1996, a B737-400 descended below its assigned level in one of the holding patterns at London Heathrow, in IMC, to within 100 feet vertically and between 680 and 820 metres horizontally of a MD-81 at its correct level. Neither aircraft was fitted with ACAS.)
- A310, vicinity Birmingham UK, 2006 (LB CFIT HF) (On 24 November 2006, an A310 descended significantly below cleared altitude during a radar vectored approach positioning, as a result of the flight crew's failure to set the QNH, which was unusually low.)
- B763, en route North Bay Canada, 2009 (LOC HF AW LOS) (On 19 June 2009 a Boeing 767-300 being operated by Polish carrier LOT on a scheduled passenger flight from Chicago O’Hare to Warsaw was in the cruise at FL330 feet in night IMC when one of the air speed indicators suddenly displayed a false high reading, which triggered an over speed warning. The flight crew response was based on the presumption that the speed increase was real and thrust was reduced and the aircraft put into a climb. A stall warning followed and descent was then made.)
- … further results
"Pressure altimeter setting error" is not in the list of possible values (Accepted ATC Clearance not followed, SID bust, Clearance readback error undetected, TCAS RA response, Manual flight) for this property.
- A320, vicinity Sochi Russian Federation, 2006 (HF CFIT) (On 3 May 2006, an Airbus 320 operated by Armavia Airlines at night and in instrument meteorological conditions (IMC) mismanaged a go around and crashed into the Black Sea near Sochi Airport, Russia.)
- A320, vicinity Addis Ababa Ethiopia, 2003 (CFIT) (On 31 March 2003, an A320, operated by British Mediterranean AW, narrowly missed colliding with terrain during a non-precision approach to Addis Ababa, Ethiopia.)
- P46T, vicinity Son Bonet Palma de Mallorca Spain, 2002 (HF AI CFIT) (On 19 December 2002, a Piper PA-46 Malibu, after takeoff from Son Bonet Aerodrome, penetrated the control zone (CTR) of Palma de Mallorca tower. The pilot was instructed to leave the CTR and the aircraft headed towards mountainous terrain to the north of the island where the flight conditions were below the VFR minimum. In level flight the aircraft impacted terrain at an altitude of 2000 ft killing all three occupants.)
- EC25, vicinity ETAP Central offshore platform, North Sea UK (CFIT HF) (On 18 February 2009, the crew of Eurocopter EC225 LP Super Puma attempting to make an approach to a North Sea offshore platform in poor visibility at night lost meaningful visual reference and a sea impact followed. All occupants escaped from the helicopter and were subsequently rescued. The investigation concluded that the accident probably occurred because of the effects of oculogravic and somatogravic illusions combined with both pilots being focused on the platform and not monitoring the flight instruments.)
- EC55, en-route, Hong Kong China, 2003 (HF CFIT) (On 26 August 2003, at night, a Eurocopter EC155, operated by Hong Kong Government Flight Service (GFS), performing a casualty evacuation mission (casevac), impacted the elevated terrain in Tung Chung Gap near Hong Kong International airport.)
- … further results
"Pressure altimeter setting error" is not in the list of possible values (Into water, Into terrain, Into obstruction, No Visual Reference, Lateral Navigation Error, Vertical navigation error, VFR flight plan, IFR flight plan) for this property.
- Doc 8168 (PANS-OPS), Volume I, Flight Procedures - Part VI - Altimeter Setting Procedures - Chapter 3.
- ICAO Video: Altimetry - Basic Principles;
Flight Safety Foundation ALAR Toolkit
EUROCONTROL Level Bust Toolkit
Airbus Briefing Notes