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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:

  • 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.)
  • 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.)
  • 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.)
  • 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.)
  • DH8A/DH8C, en route, northern Canada, 2011 (LB LOS HF) (On 7 February 2011 two Air Inuit DHC8s came into head-to-head conflict en route over the eastern shoreline of Hudson Bay in non radar Class ‘A airspace when one of them deviated from its cleared level towards the other which had been assigned the level 1000 feet below. The subsequent investigation found that an inappropriate FD mode had been used to maintain the assigned level of the deviating aircraft and noted deficiencies at the Operator in both TCAS pilot training and aircraft defect reporting as well as a variation in altitude alerting systems fitted to aircraft in the DHC8 fleet.)
  • … 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.

  • 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.)
  • EC25, vicinity ETAP Central offshore platform, North Sea UK (CFIT HF) (On 18 February 2009, the crew of Eurocopter EC225 LP Super Puma attempting to make an approach to a North Sea offshore platform in poor visibility at night lost meaningful visual reference and a sea impact followed. All occupants escaped from the helicopter and were subsequently rescued. The investigation concluded that the accident probably occurred because of the effects of oculogravic and somatogravic illusions combined with both pilots being focused on the platform and not monitoring the flight instruments.)
  • 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.)
  • B734, vicinity Lyon France, 2010 (CFIT HF) (On 7 September 2010, a Turkish operated Boeing 737-400 flew a non precision approach at Lyon Saint-Exupéry in IMC significantly below the procedure vertical profile throughout and only made a go around when instructed to do so by ATC following an MSAW activation. The minimum recorded radio height was 250 feet at 1.4nm from the runway threshold.)
  • D328, Sumburgh UK, 2006 (CFIT HF) (On 11 June 2006, a Dornier 328 operated by City Star Airlines whilst positioning in marginal visibility for a day approach at Sumburgh, Shetland Isles UK, and having incorrectly responded to TAWS Class A warnings/alerts by not gaining safe altitude, came to close proximity with terrain . The approach was continued and a safe landing was made at the 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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