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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:
- A343, En route, mid North Atlantic Ocean, 2011 (LB LOC HF) (On 22 July 2011 an Air France A340-300 en route over the North Atlantic at FL350 in night IMC encountered moderate turbulence following "inappropriate use of the weather radar" which led to an overspeed annunciation followed by the aircraft abruptly pitching up and gaining over 3000 feet in less than a minute before control was regained and it was returned to the cleared level. There Investigation concluded that "the incident was due to inadequate monitoring of the flight parameters, which led to the failure to notice AP disengagement and the level bust, following a reflex action on the controls.”)
- BE20/SF34, Vicinity Stornoway UK, 2011 (LB LOS HF) (On 31 December 2011 a USAF C12 Beech King Air descended 700 feet below the cleared outbound altitude on a procedural non precision approach to Stornoway in uncontrolled airspace in IMC and also failed to fly the procedure correctly. As a result it came into conflict with a Saab 340 inbound on the same procedure. The Investigation found that the C12 crew had interpreted the QNH given by ATC as 990 hPa as 29.90 inches, the subscale setting units used in the USA. The Saab 340 pilot saw the opposite direction traffic on TCAS and descended early to increase separation.)
- 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.)
- B733, vicinity Helsinki Finland, 2008 (LB CFIT HF) (On 26 March 2008, a Ukraine International Airlines’ Boeing 737-300 being vectored by ATC to the ILS at destination Helsinki in IMC descended below its cleared altitude and came close to a telecommunications mast. ATC noticed the deviation and instructed a climb. The investigation attributed the non-compliance with the accepted descent clearance to the failure of the flight crew to operate in accordance with SOPs. The ability of ATC safety systems as installed and configured at the time of the occurrence was also noted.)
- A332, En route, near Dar es Salaam Tanzania, 2012 (LOC LB WX HF) (On 27 February 2012, an Air France Airbus A330 en route at night at FL360 and crossing the East African coast northbound at FL360 encountered sudden violent turbulence unanticipated by the flight crew and control of the aircraft was briefly lost with two minor injuries to occupants. The Investigation concluded that a rapidly developing and isolated convective cell had not been detected because of failure to make proper use of the weather radar, but noted that the actions of the crew to recover control had been appropriate and that the aircraft had remained during its flight envelope throughout.)
- … 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.
- A306, East Midlands UK, 2011 (LOC AW HF) (On 10 January 2011, an Air Atlanta Icelandic Airbus A300-600 on a scheduled cargo flight made a bounced touchdown at East Midlands and then attempted a go around involving retraction of the thrust reversers after selection out and before they had fully deployed. This prevented one engine from spooling up and, after a tail strike during rotation, the single engine go around was conducted with considerable difficulty at a climb rate only acceptable because of a lack of terrain challenges along the climb out track.)
- 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.)
- GLF4, vicinity Kerry Ireland, 2009 (CFIT HF) (On 13 July 2009, a Gulfstream IV being operated by Indian operator Asia Aviation on a private flight from Kerry to Luton with one passenger on board in day IMC suffered a left main windshield failure shortly after take off and elected to make a return to land. Having received an ATC clearance to do so, it then failed to follow it and began a steep descent approximately 6 nm to the south of the airport towards high ground. When ATC became aware of this, an urgent instruction to climb was given and eventually the return was completed.)
- BE20, vicinity Gallatin Field MT USA, 2007 (CFIT HF) (On February 6, 2007, a Beech 200 King Air, being operated by Metro Aviation on an EMS positioning flight from Great Falls MT to Gallatin Field MT, collided at night in VMC with mountainous terrain approximately 13 nm north-northwest of the intended destination shortly after advising that the airport was in sight and requesting and obtaining permission for a visual approach.)
- DH8D, Vicinity Exeter UK, 2010 (CFIT LB AW HF) (On 11 September 2010, a DHC8-400 being operated by Flybe on a scheduled passenger flight from Bergerac France to Exeter failed to level as cleared during the approach at destination in day VMC and continued a premature descent without the awareness of either pilot due to distraction following a minor system malfunction until an EGPWS ‘PULL UP’ Hard Warning occurred following which a recovery climb was initiated. There were no abrupt manoeuvres and no injuries to any of the 53 occupants.)
- … 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