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Altimeter Setting Procedures

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Article Information
Category: Level Bust Level Bust
Content source: SKYbrary About SKYbrary
Content control: EUROCONTROL EUROCONTROL

Contents

Description

The aircraft altimeter barometric sub-scale must be set to the appropriate setting for the phase of flight. These are:

  • 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

altimeter setting
Altimeter Setting

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.

Effects

Defences

Effective SOPs contained in company flight operations manuals which specify appropriate procedures for the setting and cross-checking of altimeter barometric sub scales.

Typical Scenarios

  • 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.

Solutions

  • 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.

Related Articles

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:

  • 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.)
  • 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.)
  • 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.)
  • 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.)
  • A319 / B744, en route near Oroville WA USA, 2008 (WAKE HF AW) (On 10 January 2008, an Air Canada Airbus A319 en route over the north western USA encountered unexpected sudden wake vortex turbulence from an in trail Boeing 747-400 nearly 11nm ahead to which the pilots who then responded with potentially hazardous flight control inputs which led to reversion to Alternate Control Law and aggravated the external /disturbance to the aircraft trajectory with roll up to 55° and an unintended descent of 1400 feet which with cabin service in progress and sea belt signs off led to cabin service carts hitting the cabin ceiling and several passenger injuries, some serious.)
  • … further results

warning.png"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.

  • LJ35, vicinity Masset BC Canada, 1995 (CFIT HF) (On 11 January 1995, a Learjet 35, crashed into the sea while conducting an NDB approach to Masset, British Columbia, Canada. The most probable cause was considered to be a miss-set altimeter.)
  • 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.)
  • C185, Smithers BC Canada, 2000 (CFIT) (On 27 September 2000, a Cessna 185, struck a snow covered hillside, probably while in controlled flight, en-route from Smithers BC, Canada.)
  • B738, vicinity Denpasar Bali Indonesia, 2013 (CFIT HF) (On 13 April 2013, a Lion Air Boeing 737-800 flew a day non precision approach to runway 09 at Bali (Denpasar) and after encountering deteriorating visibility conditions continued below MDA before impacting the sea short of the intended landing runway after a go around had been called following the EGPWS ‘Twenty’ call. The aircraft broke up on impact but there was no fire and all 108 occupants survived with only 4 sustaining serious injury. An investigation is continuing.)
  • A320, vicinity Glasgow UK, 2008 (CFIT HF) (An Airbus A322 being operated by British Airways on a scheduled passenger flight from London Heathrow to Glasgow was being radar vectored in day IMC towards an ILS approach to runway 23 at destination when an EGPWS Mode 2 Hard Warning was received and the prescribed response promptly initiated by the flight crew with a climb to MSA.)
  • … further results

warning.png"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.

Further Reading

ICAO

  • 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

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