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Altimeter Setting Procedures
From SKYbrary Wiki
- 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:
- 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.)
- F15 / E145, en-route, Bedford UK, 2005 (LB AI LOS AGC HF) (On 27 January 2005, two USAF-operated McDonald Douglas F15E fighter aircraft, both continued to climb and both passed through the level of an Embraer 145 being operated by British Airways Regional on a scheduled passenger flight from Birmingham to Hannover, one seen at an estimated range of 100 feet.)
- 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.)
- A319 / A321, en-route, west north west of Geneva, Switzerland 2011 (LOS LB HF) (On 6 August 2011 an Easyjet Airbus A319 on which First Officer Line Training was in progress exceeded its cleared level during the climb after a different level to that correctly read back was set on the FMS. As a result, it came into conflict with an Alitalia A321 and this was resolved by responses to coordinated TCAS RAs. STCA alerts did not enable ATC resolution of the conflict and it was concluded that a lack of ATC capability to receive Mode S EHS DAPs - since rectified - was a contributory factor to the outcome.)
- B738, en-route, Arabian Sea, 2010 (LOC LB HF) (On 26 May 2010, a Boeing 737-800 being operated by Air India Express on a passenger flight from Dubai UAE to Pune, India was in the cruise at night at FL370 near PARAR when a sudden high speed descent occurred without ATC clearance during which nearly 7000 feet of altitude was lost in a little over 30 seconds before recovery was made. The remainder of the flight was uneventful. Despite the abnormal pitch, pitch change and ‘g’ variation, none of the 113 occupants had been injured.)
- … 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.
- 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.)
- 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.)
- BE20, vicinity Glasgow UK, 2012 (CFIT LB HF) (On 15 September 2012, the crew of a Beech Super King Air making an ILS approach to runway 23 at Glasgow became temporarily distracted by the consequences of a mis-selection made in an unfamiliar variant of their aircraft type and a rapid descent of more than 1000 feet below the 3500 feet cleared altitude towards terrain in IMC at night followed. An EGPWS ‘PULL UP’ Warning and ATC MSAW activation resulted before the aircraft was recovered back to 3500 feet and the remainder of the flight was uneventful.)
- B738, vicinity Cork Ireland, 2006 (CFIT HF) (On 4 June 2006, a Boeing 737-800 being operated by Ryanair on a passenger flight from London Stansted to Cork became too high to land off a day visual approach and requested a right hand orbit to reposition. This positioning was flown too close to terrain with TAWS alert triggered prior to a second approach to a successful landing.)
- 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.)
- … 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.
- 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