Description

On 6 February 1996, a Boeing 757-200 (TC-GEN) being operated by Turkish airline Birgenair was on a scheduled international passenger flight from Puerto Plata to Frankfurt for wholly owned subsidiary Alas Nacionales (National Wings) as ALW311 with an augmented crew with the immediate destination a technical stop at Gander en-route first to Berlin Schönefeld. Contact with ATC was lost shortly after an apparently normal night VMC takeoff and it was subsequently found to have crashed into the sea at speed less than five minutes later 14nm northeast of the airport, resulting in the destruction of the aircraft and fatal injuries to all 189 occupants.

Investigation

An Investigation was carried out by an Accident Investigation Board (JIAA) of the General Directorate of Civil Aviation assistance from the NTSB. The FDR and CVR were both recovered from the seabed by the US Navy who engaged a specialist contractor for the task. All relevant recorded data was successfully downloaded from both recorders.

It was found that the 62 year-old Captain, who was PF for the accident flight, had a total of 24,750 hours flying experience of which 1,875 hours were on type. The 34 year-old First Officer had a total of 4461 hours flying experience of which 3,500 hours were on type. The 51 year-old Relief Captain had a total of 15,050 hours flying experience of which just 121 hours were on type.

What Happened

The airline had to allocate an aircraft and crew to the flight at short notice after the Boeing 767 which it had been planned would operate the flight had been declared unserviceable. The new crew were advised of the duty “between two and four hours before the departure time” and there was a further delay at the airport awaiting the final member of the cabin crew.

During the takeoff roll on runway 07, the First Officer made the standard 80 knots call and initially received the standard response from the Captain “checked” (which is conditional on both primary altimeters reading the same). He then immediately followed this response with “my speed isn’t working” and asked the First Officer to read out speeds from his ASI to complete the takeoff.

Approaching 600 feet agl, the Captain appeared to be persuaded that his ASI, which was now beginning to show a reading, was working. At an altitude of 3,500 feet, the Captain called for the central AP to be engaged and this was followed by the A/T and annunciation of the VNAV and LNAV modes and an EICAS ‘MACH/SPD TRIM’ message. Whilst the Captain was then recorded saying that “something abnormal was happening”, he didn’t respond to the situation and 15 seconds later was recorded repeating the same thing. This time, the First Officer voiced his agreement and told the Captain that his ASI was indicating 200 knots but decreasing. At this time, the aircraft was at 5,344 feet with a ground speed of 327 knots indicated on both pilots’ EFIS screens and a pitch attitude of 15.1 degrees nose up. The Captain responded by saying that the two indicators were wrong and asking “what can we do?” before ordering the immediate checking of the circuit breakers.

After a further fifteen seconds, the Captain remarked to the effect that when an aircraft remains on the ground for a while, it’s usual for something such as asymmetry of the elevators or similar things to happen, adding "we don't believe them” (the annunciated EICAS messages). Half a minute later ,with the groundspeed indicating 352 knots and an unchanged pitch attitude of +15.1 degrees, the aural “overspeed” warning was activated followed by the Captain commenting that this “didn’t matter” and instructing the First Officer to trip its circuit breaker and silence it. 

After a further half minute, the stick shaker can be heard. The central AP remained engaged but both the A/T and the VNAV mode were disconnected. But as the aircraft passed 7132 feet with a pitch attitude 18.3° nose up, both engines were at idle thrust. Five seconds later, the nose up pitch peaked at 21.0° and thrust was restored to both engines as the AP was disengaged. The nose up attitude immediately reduced to 5° but after a height loss of just over 1,000 feet was restored to 14.4° nose up and thrust was brought back to idle. 

The Investigation concluded that “great confusion reigned”. The Captain was recorded saying "we're not climbing, what can I do?" despite having idle thrust set. The First Officer answered “you must stop the descent, I am selecting the altitude hold” but without the AP being engaged this had no effect. Only after another 20 seconds was the Captain recorded “asking about the position of the thrust levers” and when the First Officer replied that both were at idle, the Captain immediately called "thrust, thrust” and the First Officer complied and confirmed doing so although the left thrust lever (only) was then immediately retarded to idle as height continued to rapidly decrease.

A few seconds later, the pitch attitude was recorded as rapidly increasing through 50° nose down and the left bank angle as almost 100° with thrust asymmetry maintained. The GPWS Warning ‘WHOOP, WHOOP, PULL UP’ began and two seconds later impact with the sea surface followed approximately 14 nm northeast of Puerto Plata airport.

Why It Happened

The first - and normal - opportunity to avoid the accident outcome was for the PF Captain to have rejected the takeoff when he realised that his ASI was not working. In fact the Investigation confirmed that, as should be the case with correctly calculated takeoff performance anyway, a successful rejected takeoff would have been possible up to V1.

The second reason why control of the aircraft with only a single malfunctioning instrument, the Captain’s ASI, quickly became problematic appeared to be a gross failure to establish the implications for aircraft control of this single failure. There was no attempt to refer to the standby ASI to confirm that the First Officer’s ASI was giving correct readings but the Captain’s was not.

The apparently collective confusion amongst all three pilots - and a lack of ‘informed leadership’ from the Captain - then appeared, on the basis of recorded data, to have increased as the association between pitch attitude and thrust setting seemed to be overlooked.

In particular, there was no evidence that the applicable QRH procedure - ‘Flight with Unreliable Relative Airspeed’ - was ever considered let alone actioned and instead the idea of tripping particular circuit breakers to see what happened was about as far as it got.

However, as per the ultimate conclusion of the Investigation, the final outcome of the flight was merely facilitated by what had already happened and it was the approach to an aerodynamic stall which provided the final opportunity to maintain control but the necessary reduction from 18° nose up pitch attitude was delayed and the basis for recovery, demonstrated as achievable by Boeing instructors in a full flight simulator using the prescribed and available procedure, was lost.

Overall, the Investigation came to the view that “the crew's misconception of the flight trajectory was the result of a lack of knowledge of the aircraft systems and a lack of procedural discipline. The terminal loss of control resulted when the flight crew failed to recognise the stick-shaker activation as an imminent warning of a stall aerodynamics because they stopped executing the procedures of the loss recovery”.

Ruled out as potential contributors to the evident flight control difficulties were any pre flight lack of airworthiness except the undetected blocked left side pitot probe and any issues which could have arisen from the prevailing weather conditions. 

  

The Investigation also drew a wider conclusion from their findings which was that this accident was “an indication that the international requirements for flight crew training have not kept pace with the growth and modernisation of the air transport industry and the development of aircraft” and that individual safety regulators should review pilot training requirements to improve proficiency.

The Probable Cause of the Accident was formally identified as “the crew's failure to recognise stick-shaker activation as an imminent warning of a stall and their failure to follow the procedures for recovery from this condition after there was confusion amongst the flight crew because of an erroneous indication of airspeed and an over speed warning”.

Three Contributory Factors were also identified:

• The poor discipline and capability of the flight crew, the absence of crew resource management in any form and the failure to comply with basic aviation procedures.
• Little flight crew knowledge of the aircraft systems including relative speed indications, the autopilot, aircraft type procedures, alternate instrument source selection and attempted flight without reference to thrust setting and pitch attitude.
• The failure of the Birgenair maintenance staff to install the pitot probe covers whilst the aircraft was parked out of service for almost three weeks and their failure to perform a required test of pitot-static system sensing prior to release to service.

As were four Additional Factors:

 

• The flight crew may not have been physically and mentally rested and prepared to operate the flight due to unexpected crew call out.
• Birgenair pilot training did not include the principles of Crew Resource Management and more generally was a combination of externally sourced training that lacked continuity and integrated approaches to maximise flight crew proficiency.
• The Birgenair Boeing 757/767 Operations Manual did not contain detailed presentation of flight crew procedures and appropriately verified checklists covering the response to a discrepancy in airspeed indications and the simultaneous activation of speedmatch or the relationship of the EICAS messages to systems, warnings and flight with unreliable airspeed.
• The EICAS system of the Boeing 757/767 aircraft did not include an alert message when an erroneous airspeed is detected.

Nine Safety Recommendations were made as a result of the Findings of the Investigation:

• that the Federal Aviation Administration (FAA) issue an Airworthiness Directive requiring that the Flight Manual for the Boeing 757/767 be revised to notify pilots that simultaneous display of the EICAS messages “MACH/SPD TRIM” and “RUDDER RATIO” is a indication of discrepancies in the air speed indication.
• that the Federal Aviation Administration (FAA) require Boeing Commercial Aircraft to modify the crew alerting system on the Boeing 757/767 to include a CAUTION when an erroneous air speed indication is detected.
• that the Federal Aviation Administration (FAA) require Boeing Commercial Aircraft to modify the Boeing 757/767 Operations Manual to include a detailed procedure on “Identification and Elimination of an erroneous speed indication” in the section on Emergencies.
• that the Federal Aviation Administration (FAA)  issue a Flight Standards Information Bulletin addressed to Operations Inspectors so that they ensure that a procedure with detailed information on “Identifying and Removing a speed indication error” is included in the Operations Manuals of Boeing 757/767 operators. 
• that the Federal Aviation Administration (FAA) issue an Aeronautical Information Bulletin notifying Operations Inspectors of the circumstances of this accident so that they ensure that emphasis is placed on the importance of recognising a malfunction of speed indication during takeoff during pilot training. 
• that the Federal Aviation Administration (FAA) ensure that all Boeing 757/767 flight simulator training includes a scenario in which the pilot is trained to respond appropriately to circumstances indicating a blocked pitot probe.
• that the International Civil Aviation Organisation (ICAO) ensures that each airline has a specific and specialised Training Manual for the type of operation carried out to complement the generic training that flight crews receive from contractors offering to carry our pilot training on their behalf.
• that the International Civil Aviation Organisation (ICAO) establishes a requirement that all commercial airlines ensure that their flight crew training program includes the use of Crew Resource Management (CRM).
• that the International Civil Aviation Organisation (ICAO) requires that existing flight crew training requirements are reviewed to increase their effectiveness.

The Final Report of the Investigation, which was prepared only in Spanish, was released on 25 October 1996 and the received comments from interested parties (no draft report was circulated) were added to the Appendices of the already-issued Final Report the following year. This Summary is based on an unofficial translation of the Final Report which is believed to have been accurate but is not so warranted.

Related Articles

• Loss of Control
• Unreliable Airspeed Indications
• Air Speed Indicator
• Rejected Takeoff
• EFIS
• Standard Operating Procedures
• Crew Resource Management
• Aerodynamic Stall
• Recovery from Unusual Aircraft Attitudes