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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:
- GLF5 / A319, south-eastern France, 2004 (LB LOS HF) (On 16 September 2004, a loss of separation occurred over Geneva between Air France A319 and a Gulfstream 5 which commenced descent without clearance by ATC and with coordinated TCAS RAs not followed by either aircraft.)
- 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.)
- C525 / B773, vicinity London City UK, 2009 (LB LOS AGC HF) (On 27 July 2009, a Cessna 525 departing from London City failed to comply with the initial 3000 ft QNH SID Stop altitude and at 4000 ft QNH in day VMC came into close proximity on an almost reciprocal heading with a Boeing 777-300ER. Actual minimum separation was approximately 0.5nm laterally and estimated at between 100 ft and 200 ft vertically.)
- 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.)
- A320, En route, north of Swansea UK, 2012 (LB HF) (On 7 September 2012, the crew of an Aer Lingus Airbus A320-200 mis-set their descent clearance. When discovering this as the actual cleared level was being approached, the AP was disconnected and the unduly abrupt control input made led to an injury to one of the cabin crew. The original error was attributed to ineffective flight deck monitoring and the inappropriate corrective control input to insufficient appreciation of the aerodynamic handling aspects of flight at high altitude. A Safety Recommendation to the Operator to review relevant aspects of its flight crew training was 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.
- RJ1H, vicinity Zurich Switzerland, 2001 (CFIT FIRE HF) (On 24 November 2001, a Crossair Avro RJ100 making a night non precision approach to Zurich violated approach minima and subsequently impacted terrain whilst making a delayed attempt to initiate a go around. The aircraft was destroyed by the impact and post crash fire and 24 of the 33 occupants were killed. The Investigation attributed the crash to the crew deliberately continuing descent below MDA without having acquired the prescribed visual reference. Both crew pairing and aspects of the crew as individuals were identified as the context.)
- B733, vicinity Chambery France, 2010 (CFIT LOC HF) (On 7 February 2010, a Boeing 737-300 being operated by Jet2 on a scheduled passenger flight from Leeds/Bradford UK to Chambery France was making an ILS approach to runway 18 at destination in day IMC when a Mode 2 EGPWS ‘Terrain, Pull Up’ Warning occurred. A climb was immediately initiated to VMC on top and a second ILS approach was then made uneventfully. Despite extreme pitch during the early stages of the pull up climb, none if the 109 occupants, all secured for landing, were injured.)
- DH8A, vicinity Palmerston North New Zealand, 1995 (CFIT HF AW) (On 9 June 1995 a de Havilland DHC-8-100 collided with terrain some 16 km east of Palmerston North aerodrome while carrying out a daytime instrument approach. The airplane departed Auckland as scheduled Ansett New Zealand flight 703 to Palmerston North airport.)
- C550, vicinity Cagliari Sardinia Italy, 2004 (CFIT HF) (On 24 February 2004, a Cessna 550 inbound to Cagliari at night requested and was approved for a visual approach without crew awareness of the surrounding terrain. It was subsequently destroyed by terrain impact and a resultant fire during descent and all occupants were killed. The Investigation concluded that the accident was the consequence of the way the crew conducted the flight in the absence of adequate visual references and with the possibility of a ‘black hole’ effect. It was also noted that the aircraft was not fitted, nor required to be fitted, with TAWS.)
- AT45, vicinity Sienajoki Finland, 2007 (LOC CFIT HF) (On 1 January 2007, the crew of a ATR 42-500 carried out successive night approaches into Seinajoki Finland including three with EGPWS warnings, one near stall, and one near loss of control, all attributed to poor flight crew performance including use of the wrong barometric sub scale setting.)
- … 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