Accident and Serious Incident Reports: LB

Accident and Serious Incident Reports: LB

Definition

Accident and Serious Incident Reports relating to accidents which involved Level Bust

The events are organised under the following sub-categories:

Accepted ATC Clearance not Followed

On 29 April 2021, the crew of an Airbus A319 which had just taken off from runway 18 at St Petersburg saw a Cessna M337 about to cross their intended track close to the same height and levelled off to ensure they passed beneath it achieving a 100 feet separation. The conflict was attributed to the controller’s general loss of situational awareness and his failure to properly scan airspace in the vicinity of the airport. The Cessna 337 pilot’s failure to fly at the standard circuit height or track downwind at the standard distance from the runway was deemed contributory.

On 12 January 2022, an Embraer 170 and a Cessna 525 crossed tracks without the prescribed minimum separation with neither ATC nor the Embraer crew being aware. Although ATC had issued acknowledged clearances to keep the Embraer 1,000 feet above the Cessna, it actually passed beneath it violating minimum lateral separation. The underlying cause of the event was found to be an un-rectified recurrent intermittent fault in one of the Cessna’s air data systems. Poor Cessna crew/controller communication during the event, systemically poor safety culture at its operator and shortcomings in the Textron Aircraft Maintenance Manual were considered contributory.

On 6 November 2018, an Airbus A340-600 in the cruise northbound over the Swiss Alps received an overspeed warning after encountering an unexpected wind velocity change but the crew failed to follow the prescribed response procedure. This led initially to a climb above their cleared level and further inappropriate actions were then followed by PAN and MAYDAY declarations as control of the aircraft was briefly lost in a high speed descent to below their cleared level. The operator subsequently enhanced pilot training realism by providing it in a simulator configured for the aircraft variant operated and introduced ‘upset recovery training’.

On 6 January 2018, a Boeing 737-900 and an Airbus A320 both inbound to Surabaya with similar estimated arrival times were cleared to hold at the same waypoint at FL100 and FL110 respectively but separation was lost when the A320 continued below FL110. Proximity was limited to 1.9nm laterally and 600 feet vertically following correct responses to coordinated TCAS RAs. The Investigation found that all clearances / readbacks had been correct but that the A320 crew had set FL100 instead of their FL110 clearance and attributed this to diminished performance due to the passive distraction of one of the pilots.

On 2 May 2015, a Boeing 777-200 deviating very significantly north of its normal route from Malabo to Douala at night because of convective weather had just turned towards Douala very close to 13,202 feet high Mount Cameroon whilst descending through 5000 feet, when an EGPWS TERRAIN AHEAD alert and ‘PULL UP’ warning prompted an 8,000 foot climb which passed within 2,100 feet of terrain when close to and still below the summit. The Investigation attributed the dangerous event primarily to the augmented crew’s absence of situational awareness and the operator’s failure to risk-assess the route involved.

SID Bust

On 3 July 2014, a Boeing 777-300 departing Houston came within 200 feet vertically and 0.61nm laterally of another aircraft after climbing significantly above the Standard Instrument Departure Procedure (SID) stop altitude of 4,000 feet believing clearance was to FL310. The crew responded to ATC avoiding action to descend and then disregarded TCAS 'CLIMB' and subsequently LEVEL OFF RAs which followed. The Investigation found that an inadequate departure brief, inadequate monitoring by the augmented crew and poor communication with ATC had preceded the SID non-compliance and that the crew should have followed the TCAS RAs issued.

On 27 July 2009, a Cessna 525 departing from London City failed to comply with the initial 3000 feet QNH SID Stop altitude and at 4000 feet QNH in day VMC came into close proximity on an almost reciprocal heading with a Boeing 777-300ER. The 777, on which line training was being conducted, failed to follow any of the three TCAS RAs generated. Actual minimum separation was approximately 0.5nm laterally and estimated at between 100 feet and 200 feet vertically. It was noted that the Cessna had been given a stepped climb SID.

Clearance Readback Error Undetected

On 21 March 2022, an Airbus A320 level at FL 360 lost separation with another Airbus A320 which continued its descent beyond its cleared level. A predictive conflict alert prompted the controller to issue multiple calls confirming the clearance limit but with no response so when both aircraft tracks crossed at FL 360, lateral separation was reduced to 3.8 nm. It was concluded that the immediate cause of the conflict was the failure of the descending aircraft to respond to ATC alerting calls but that its origin was an undetected incorrect readback of the descent clearance.

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.

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 only a TCAS TA, was given an emergency turn by ATC. The recorded CPA was 2.2 nm and 125 feet.

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.

On 12 April 2013, a Ryanair Boeing 737-800 took a climb clearance intended for another Ryanair aircraft on the same frequency. The aircraft for which the clearance was intended did not respond and the controller did not notice that the clearance readback had come from a different aircraft. Once the wrong aircraft began to climb, from FL360 to FL380, a TCAS RA to descend occurred due to traffic just transferred to a different frequency and at FL370. That traffic received a TCAS RA to climb. STCA was activated at the ATS Unit controlling both Ryanair aircraft.

TCAS RA Response

On 6 January 2018, a Boeing 737-900 and an Airbus A320 both inbound to Surabaya with similar estimated arrival times were cleared to hold at the same waypoint at FL100 and FL110 respectively but separation was lost when the A320 continued below FL110. Proximity was limited to 1.9nm laterally and 600 feet vertically following correct responses to coordinated TCAS RAs. The Investigation found that all clearances / readbacks had been correct but that the A320 crew had set FL100 instead of their FL110 clearance and attributed this to diminished performance due to the passive distraction of one of the pilots.

On 29 February 2020, an Airbus A320 inbound to Delhi lost separation against an outbound A320 from Delhi on a reciprocal track and the conflict was resolved by TCAS RA activation. The Investigation found that the inbound aircraft had correctly read back its descent clearance but then set a different selected altitude. Air Traffic Control had not reacted to the annunciated conflict alert and was unable to resolve it when the corresponding warning followed and it was noted that convective weather meant most aircraft were requesting deviations from their standard routes which was leading to abnormally complex workload.

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 only a TCAS TA, was given an emergency turn by ATC. The recorded CPA was 2.2 nm and 125 feet.

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.

On 3 July 2014, a Boeing 777-300 departing Houston came within 200 feet vertically and 0.61nm laterally of another aircraft after climbing significantly above the Standard Instrument Departure Procedure (SID) stop altitude of 4,000 feet believing clearance was to FL310. The crew responded to ATC avoiding action to descend and then disregarded TCAS 'CLIMB' and subsequently LEVEL OFF RAs which followed. The Investigation found that an inadequate departure brief, inadequate monitoring by the augmented crew and poor communication with ATC had preceded the SID non-compliance and that the crew should have followed the TCAS RAs issued.

Manual Flight

On 29 April 2021, the crew of an Airbus A319 which had just taken off from runway 18 at St Petersburg saw a Cessna M337 about to cross their intended track close to the same height and levelled off to ensure they passed beneath it achieving a 100 feet separation. The conflict was attributed to the controller’s general loss of situational awareness and his failure to properly scan airspace in the vicinity of the airport. The Cessna 337 pilot’s failure to fly at the standard circuit height or track downwind at the standard distance from the runway was deemed contributory.

On 6 November 2018, an Airbus A340-600 in the cruise northbound over the Swiss Alps received an overspeed warning after encountering an unexpected wind velocity change but the crew failed to follow the prescribed response procedure. This led initially to a climb above their cleared level and further inappropriate actions were then followed by PAN and MAYDAY declarations as control of the aircraft was briefly lost in a high speed descent to below their cleared level. The operator subsequently enhanced pilot training realism by providing it in a simulator configured for the aircraft variant operated and introduced ‘upset recovery training’.

On 2 May 2015, a Boeing 777-200 deviating very significantly north of its normal route from Malabo to Douala at night because of convective weather had just turned towards Douala very close to 13,202 feet high Mount Cameroon whilst descending through 5000 feet, when an EGPWS TERRAIN AHEAD alert and ‘PULL UP’ warning prompted an 8,000 foot climb which passed within 2,100 feet of terrain when close to and still below the summit. The Investigation attributed the dangerous event primarily to the augmented crew’s absence of situational awareness and the operator’s failure to risk-assess the route involved.

On 27 February 2012, the crew of an Airbus A330 en route at night and crossing the East African coast at FL360 encountered sudden violent turbulence as they flew into a convective cell not seen on their weather radar and briefly lost control as their aircraft climbed 2000 feet with resultant minor injuries to two occupants. The Investigation concluded that the isolated and rapidly developing cell had not been detected because of crew failure to make proper use of their weather radar, but noted that activation of flight envelope protection and subsequent crew action to recover control had been appropriate.

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.

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