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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:
- A310 / B736, en-route, Southern Norway, 2001 (LB LOS HF) (On 21 February 2001, a level bust 10 nm north of Oslo Airport by a climbing PIA A310 led to loss of separation with an SAS B736 in which response to a TCAS RA by the A310 not being in accordance with its likely activation (descend). The B736 received and correctly actioned a Climb RA.)
- DH8D, vicinity Edinburgh UK, 2008 (LB CFIT HF) (On 23 December 2008, a DHC8-400 being operated by Flybe on a scheduled passenger flight from Southampton to Edinburgh continued descent below its cleared altitude of 2100ft in day VMC prior to and then whilst tracking the ILS LLZ for Runway 23 at destination. It remained below the ILS GS until the ATC GND Controller, who had no formal responsibility for this phase of flight but was positioned alongside the TWR Controller, observed that aircraft had descended to within 800 ft of local terrain approximately 5 nm from the runway threshold. The flight crew appeared unaware of this when making a ‘Finals’ call to TWR at 5.5 nm and so the Controller queried the descent. The aircraft was then levelled to achieve 600ft agl at 4nm from the threshold and an uneventful landing subsequently followed.)
- B733, vicinity Manchester UK, 1997 (LB CFIT HF) (On 1 August 1997, an Air Malta B737, descending for an approach into Manchester UK in poor weather, descended significantly below the cleared and correctly acknowledged altitude, below MSA.)
- A320, vicinity Oslo Norway, 2008 (CFIT LB HF AGC) (On 19 December 2008, an Aeroflot Airbus A320 descended significantly below its cleared and acknowledged altitude after the crew lost situational awareness at night whilst attempting to establish on the ILS at Oslo from an extreme intercept track after a late runway change and an unchallenged incorrect readback. The Investigation concluded that the response to the EGPWS warning which resulted had been “late and slow” but that the risk of CFIT was “present but not imminent”. The context for the event was considered to have been poor communications between ATC and the aircraft in respect of changes of landing runway.)
- 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.”)
- … 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.
- A333, vicinity Wom Guam Airport, Guam, 2002 (CFIT HF) (On 16 December 2002, approximately 1735 UTC, an Airbus A330-330, operating as Philippine Airlines flight 110, struck power lines while executing a localizer-only Instrument Landing System (ILS) approach to runway 6L at A.B. Pat Won Guam International Airport, Agana, Guam. Instrument meteorological conditions prevailed during the approach. Following a ground proximity warning system (GPWS) alert, the crew executed a missed approach and landed successfully after a second approach to the airport.)
- T154, vicinity Svalbard Norway, 1996 (CFIT HF) (On 29 August 1996, a Tu-154, crashed after misflying an off-set LLZ non-precision approach to Svalbard Longyear airport, Norway, in IMC.)
- B773, vicinity Melbourne Australia, 2011 (CFIT HF) (On 24 July 2011, a Thai Airways International Boeing 777-300 descended below the safe altitude on a night non-precision approach being flown at Melbourne and then failed to commence the go around instructed by ATC because of this until the instruction had been repeated. The Investigation concluded that the aircraft commander monitoring the automatic approach flown by the First Officer had probably experienced ‘automation surprise’ in respect of the effects of an unexpected FMS mode change and had thereafter failed to monitor the descent of the aircraft with a selected FMS mode which was not normally used for approach.)
- 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.)
- C30J, en-route, northern Sweden 2012 (CFIT HF FIRE) (On 15 March 2012, a Royal Norwegian Air Force C130J-30 Hercules en route on a positioning transport flight from northern Norway to northern Sweden crossed the border, descended into uncontrolled airspace below MSA and entered IMC. Shortly after levelling at FL 070, it flew into the side of a 6608 foot high mountain. The Investigation concluded that although the direct cause was the actions of the crew, Air Force procedures supporting the operation were deficient. It also found that the ATC service provided had been contrary to regulations and attributed this to inadequate controller training.)
- … 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