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ASN Wikibase Occurrence # 235618
Last updated: 30 April 2020
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Date:09-JUN-2019
Time:15:59
Type:Silhouette image of generic B744 model; specific model in this crash may look slightly different
Boeing 747-436
Owner/operator:British Airways
Registration: G-BNLN
C/n / msn: 24056/802
Fatalities:Fatalities: 0 / Occupants: 338
Other fatalities:0
Aircraft damage: None
Category:Serious incident
Location:N of Blackburn -   United Kingdom
Phase: En route
Nature:International Scheduled Passenger
Departure airport:London-Heathrow Airport (LHR/EGLL)
Destination airport:Phoenix-Sky Harbor International Airport, AZ (PHX/KPHX)
Investigating agency: AAIB
Narrative:
British Airways flight BA289, a Boeing 747-400, was on a scheduled flight from London to Phoenix, USA, with the commander and co-pilot being line-checked by a training captain, who occupied the jump seat. The aircraft took off at 14:28 hrs with the co-pilot acting as pilot flying (PF). It had just reached the top of climb at FL330, with the right autopilot and autothrottle engaged, when the Master Warning activated. The crew reported that a line appeared through the Vertical Navigation (VNAV) path on the Flight Mode Annunciator (FMA) and that the Engine Indication and Crew Alerting System (EICAS) indicated a red overspeed warning, ALT disagree, IAS disagree, Rudder Ratio Single, Airspeed Low and Altitude Alert. The crew also reported feeling ear discomfort from a change in cabin air pressure.
The co-pilot recognised the airspeed had become unreliable, notifying the other two pilots before carrying out the recall drill. In doing so, he noted that the autothrottle had reduced thrust to 1.2 EPR before it was disengaged. He set a pitch of 4° nose-up and thrust of 80% N1, as required by the drill.
The crew declared a PAN with ATC and were cleared to remain on their current heading with a block altitude cleared for them to operate within. The commander and training captain then referred to the “Unreliable Airspeed Table” in the Quick Reference Handbook (QRH) from which they determined the required pitch attitude under the prevailing conditions was 3.5° nose-up and the required thrust setting was 87.5% N1.
While the datums were being agreed, and with the aircraft maintaining a pitch attitude of 4° nose-up and engine power setting of 80% N1, the stick shakers activated. The crew briefly discussed whether to maintain the ‘Airspeed Unreliable’ datums or carry out the stall recovery manoeuvre. They agreed that the stall recovery would be appropriate, and this was carried out by the co-pilot. He decreased the pitch attitude to 1° nose-down, at which point the stall warning ceased, which the crew considered confirmed their belief that the stall warning was genuine. He then slowly increased the pitch and engine power to the datums required in the QRH, however, as he did so the stall warning reoccurred, so the co-pilot reduced pitch again until the warning ceased. As the airspeed increased, the co-pilot gradually increased pitch, however the stick shaker activated once again, causing him to reduce the pitch angle until it stopped activating. He repeated this process several times until the QRH datums were finally attained and there were no further stick shaker activations.
The aircraft had lost about 2,800 ft during these manoeuvres. With the aircraft now stable, the crew completed the rest of the ‘Airspeed Unreliable’ checklist with the air data source being changed from the right to the centre Air Data Computer (ADC). This allowed the autopilot and autothrust to be re-engaged. The crew also contacted the operator’s maintenance office by radio which was able to confirm, via the aircraft health monitoring system, that the right ADC had failed.
The crew and maintenance office both assured themselves that the aircraft was still able to comply with the Required Navigation Performance and Minimum Navigation Performance
Specifications and, having done so, the flight continued to the destination with no further incidents.

Sources:

AAIB
https://www.flightradar24.com/data/aircraft/g-bnln#20d41eac

Accident investigation:
cover
  
Investigating agency: AAIB
Status: Investigation completed
Duration: 10 months
Download report: Final report


Images:

Photo of G-BNLN courtesy AirHistory.net


London - Heathrow (EGLL / LHR)
14 March 2019; (c) Lewis Grant


Discrepancy between the right and left ADC (AAIB)

Revision history:

Date/timeContributorUpdates
30-Apr-2020 16:48 harro Added
30-Apr-2020 16:52 harro Updated [Photo, Accident report, ]

Corrections or additions? ... Edit this accident description