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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.
altimeter setting
Altimeter Setting

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.

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 depending 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 depending 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 and consequently that the aircraft is likely to be closer, and possibly a lot closer, to the ground than with QNH set.

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:

  • 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.)
  • 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.)
  • 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.

  • A310, vicinity Abidjan Ivory Coast, 2000 (CFIT HF) (On 30 January 2000, an Airbus 310 took off from Abidjan (Ivory Coast) at night bound for Lagos, Nigeria then Nairobi, Kenya. Thirty-three seconds after take-off, the airplane crashed into the Atlantic Ocean, 1.5 nautical miles south of the runway at Abidjan Airport. 169 persons died and 10 were injured in the accident.)
  • MD83, vicinity Paris Orly France, 1997 (CFIT HF) (On 23 November 1997, a McDonald Douglas MD 83 being operated by AOM French Airlines on a scheduled passenger flight from Marseille to Paris Orly made an unintended premature descent almost to terrain impact at 4nm from the destination runway in day IMC before a go around was commenced. A subsequent approach was uneventful and a normal landing ensued. There was no damage to the aircraft or injury to the 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.)
  • E145, en route, north east of Madrid Spain, 2011 (CFIT LB HF AGC) (On 4 August 2011, a Luxair Embraer 145 flying a STAR into Madrid incorrectly read back a descent clearance to altitude 10,000 feet as being to 5,000 feet and the error was not detected by the controller. The aircraft was transferred to the next sector where the controller failed to notice that the incorrect clearance had been repeated. Shortly afterwards, the aircraft received a Hard EGPWS ‘Pull Up’ Warning and responded to it with no injury to the 47 occupants during the manoeuvre. The Investigation noted that an MSAW system was installed in the ACC concerned but was not active.)
  • 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

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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