37.5 degree angle of bank, one engine out, gear down and at 500 feet
Emergency Landing After Bird Strike
On 6 June 2010, a Boeing 737-400 aircraft struck a flock of geese shortly after take off from Schiphol airport in the Netherlands and subsequently completed an emergency landing. The final report on the investigation into the event, has highlighted the importance of adherence to SOPs, bird hazard management, and the need for ATC to pass information about obstacles to aircraft flying below minimum vectoring altitude.
Description
On 6 June 2010, a Boeing 737-400 being operated by Atlas Blue, a wholly owned subsidiary of Royal Air Maroc, on a passenger flight from Amsterdam to Nador, Morocco encountered a flock of geese just after becoming airborne from runway 18L in day VMC close to sunset and lost most of the thrust on the left engine following bird ingestion. A MAYDAY was declared and a minimal single engine climb out was followed by very low level visual manoeuvring not consistently in accordance with ATC radar headings before the aircraft landed back on runway 18R just over 9 minutes later. The aircraft was stopped on the runway where inspection found the right main gear tyres deflated as a result of the high brake unit temperature developed during heavy braking and extensive bird remains in the left main and nose gear bays and in the avionics bay. None of the 162 occupants were injured and the passengers were disembarked using steps brought to the aircraft before being bussed to the terminal.
Investigation
An Investigation was carried out by the Dutch TSB. The FDR and 2 hour CVR recordings were recovered and available to the Investigation. A cross connection in the CVR which had resulted in a 30 minute limit to the CAM channel and a 2 hour limit to the Cabin PA channel instead of the correctly wired opposite was found but was of no consequence to the work of the Investigation.
Extensive damage was found to have been caused internally and externally to the left engine and dents were found in the leading edge of the vertical stabiliser and the lower fuselage. The geese hit, subsequently identified as Canada Geese, were advised as having a mass in summer of between 3 and 5 kg which meant that their weight significantly exceeded the certification requirement for the CFM56-3 engine involved which was to withstand ingestion of a single 1.8 kilogram bird. It was noted that the current enhanced bird ingestion certification criterion for CFM56-sized engines is a single 2.75 kg bird, still less than the mass of those encountered.
It was established that, after a routine reduced thrust take off, the geese had been struck at 16 feet4.877 m above the runway as gear retraction was initiated. A few seconds later, the aircraft commander ordered the First Officer to select the landing gear (which was still in transit) down and declare an emergency to ATC. These actions were taken and radar vectors were requested from ATC. Left engine thrust had immediately reduced to about 45% N1, a negligible amount, and remained at that level until memory actions for engine shutdown were completed approximately four minutes later. The cleared SID had been for a left turn on reaching 500 feet152.4 m agl but, with the landing gear down and a manual reduction in the thrust set on the functioning right engine, rate of climb had been low and at 280 feet85.344 m agl, a turn had been commenced to the right without reference to ATC who had to stop a take off on runway 24 to prevent a conflict. The right turn towards north reached a maximum bank angle of 37.5° and minimum speed of 156 kt288.912 km/h
80.184 m/s IAS, just below the applicable V2 speed, and the aircraft eventually reached a height of just under 500 feet152.4 m agl. From there, a slow descent had begun which only stopped at 352 feet107.29 m following the first of many GPWS activations, in this instance Mode 3 “DON’T SINK”.
Thereafter, the track and altitude flown was persistently erratic and had been accompanied by frequent and sometimes continued GPWS activations as the aircraft passed obstructions or began to descend towards built up areas of Amsterdam. An annotated depiction of the circuit flown is provided in a composite diagram in the Official Report. Height above the ground during the positioning prior to arriving on a final approach to runway 18R varied between 348 feet agl and 629 feet agl. For most of the first four minutes of the flight, prior to the delayed completion of the memory actions for shutdown of the failed left engine, the aircraft was noted to have remained below 500 feet agl.
Throughout, ATC issued radar vectors as requested and the aircraft commander visually avoided obstacles whilst continuing to fly the aircraft manually. ATC had no depiction of terrain or obstacles on their radar and it was noted that the MRVA of 1200 feet365.76 m agl within the Schiphol CTZ. In respect of the issue of radar vectors below MRVA, it was noted that a previous generic review of the risk to persons on the ground had not considered “the risks of advising aircraft in distress below the minimum vectoring altitude, in particular when the visibility becomes outside (the) visual meteorological conditions. In this respect the absence (of) high obstacles on the radar screen increased the imposed risk during the emergency situation. (The ANSP) has no procedure for air traffic controllers that allows for guidance to aircraft in distress in such a situation (and) has not considered the risks of assisting aircraft in distress that are flying below the minimum vectoring altitude in the Schiphol control zone.
The Investigation further found that:
“Air traffic controllers do not know the (exact) location and height of high obstacles in the Schiphol control zone, or cannot know this information because it is not presented on their radar screens. However, controllers do provide headings to aircraft in distress that are flying below minimum vectoring altitude, regardless of the visibility conditions. As a result, aircraft that are flying outside visual meteorological conditions could, if the worst comes to the worst, collide with a high obstacle. In other words, in such a case the ‘assist’ principle would not have contributed to preventing a collision. Although the likelihood of such an emergency is small, the potential consequences are huge, rendering the risk level unacceptable. The fact that crew members do not always follow the instructions and advice provided by air traffic control during an emergency does not diminish this conclusion.”
However, it was concluded that “the threat of this (particular event) for the residents around Schiphol was mainly caused by the crew not observing the ‘initial climb – one engine inoperative’ procedure”.
On the possible value of tactical detection of birds by radar, the Investigation concluded that:
“Further studies should be conducted to assess the operational implementation and applications of radar detection at civil aviation airports. This should also include efforts to identify the responsibilities of the parties involved in radar bird detection, and the extent to which these parties are authorised and at liberty to intervene in flight operations in order to reduce the risk of bird strikes.”
The formal statement of Conclusions of the Investigation was as follows:
Causal Factors
§ Shortly after take-off a bird strike occurred which caused damage to the left engine and reduced thrust to approximately 45%. The flight crew then took the right decision to return to Schiphol airport.
§ However, this decision was not executed in accordance with standard operational procedures. The deviations from the standard operational procedures after an engine failure were:
§ The initiation of a (right) turn at 280 feet with a bank angle of up to 37.5 degrees instead of climbing to the prescribed ‘clean up’ altitude with retracted landing gear.
§ Selecting gear down at very low altitude after it had first been selected up.
§ Reducing the thrust on the undamaged right engine from 94% N1 to 83% N1 instead of selecting maximum thrust.
These deviations from the standard operational procedures resulted in the aircraft only being able to achieve a limited rate of climb, causing it to be unable to achieve the required minimum safe flying altitude. The flight crew had difficulty controlling the aircraft and were distracted by various audio and visual warnings in the cockpit which were the consequence of incorrectly completed cockpit procedures.
Contributing factors
§ During the flight, the crew resource management and crew communication were not in accordance with the international standard for airline pilots.
§ The immediately-initiated right turn and the marginal remaining flying performance made the tasks more difficult and led to complications which meant that both pilots were unable to fulfil their tasks, such as the completion of cockpit procedures and checklist readings, in the prescribed manner. This in turn led to new complications such as unnecessary warnings and an unstable flight path.
§ During the refresher training for Atlas Blue and Royal Air Maroc pilots, they were not trained to deal with multiple malfunctions during the flight.
§ Prior to every recurrent training pilots of Atlas Blue and Royal Air Maroc were taught about the specific malfunctions that would occur. This is not unusual in the context of flight training practice, but the consequence was that the pilots did not learn how to respond to unexpected effects.
§ Dealing with multiple malfunctions featured only in the initial training for Captains.
§ Although the Flight Crew Training Manual and the Flight Crew Operations Manual contain the procedures and checklists required for the adequate tackling of malfunctions which occurred during this flight, the flight crew and the training managers of Atlas Blue and Royal Air Maroc regarded this serious incident as a unique event which pilots cannot be trained in.
§ The analysis of measures implemented in response to the (third party risk) investigation (initiated in response to the recommendation by the Bijlmermeer Air Disaster Parliamentary Board of Inquiry) failed to take account of the risks caused by aircraft in distress situations flying below the minimum vectoring altitude. These aircraft are given headings in the Schiphol Control Zone, despite the fact that air traffic controllers do not have information on high obstacles in the flight path. This unnecessarily increases the risk of a collision. This problem is all the more urgent when aircraft are flying outside visual meteorological conditions.
§ The investigation conducted by (ANSP) Air Traffic Control the Netherlands in response to the recommendation by the Bijlmermeer Air Disaster Parliamentary Board of Inquiry has resulted in a policy framework on the supervision of aircraft in distress situations and on flying over densely populated areas. According to this policy framework for aircraft in distress situations, the captain is responsible for flight operation while the air traffic controller provides assistance to the cockpit crew. Aircraft in distress must use existing runway arrival and departure routes where possible, which limits the amount of flying over densely populated areas. The Directorate-General of Aviation and Maritime Affairs has approved the aforementioned policy framework. As a result of this policy framework, densely populated areas are not presented on air traffic controllers’ radar screens.
§ Schiphol airport is practically surrounded by a great number of populated/built-up areas. The consequences of flying lower than the minimum vectoring altitude are (considerable). This is particularly the case when flying outside visual meteorological conditions.
§ The maximum height above the ground of the aircraft during the flight was 730 feet and this was well under the minimum vectoring altitude for Schiphol of 1200 feet.
§ Only two obstacles are displayed on the radar screen, of which one is in the Schiphol control zone (whereas) there are a number of other obstacles which might pose a risk to aircraft flying lower than the minimum vectoring altitude. This is particularly the case when flying outside visual meteorological conditions.
§ The presence of one or more birds with a large total mass in the flight path of an aircraft is a risk to flight safety. This particularly applies to geese due to their considerable mass and because they fly in groups. Most bird strikes occur during the take-off and landing phases of the flight.
§ The Investigation has shown that parties that have a direct influence on bird control at Schiphol airport have exhausted their options. Except for the closing of active runways more often, it is up to other parties, therefore, to take further measures to reduce the safety risk caused by bird strikes.
§ All the aviation, agricultural, and bird and environmental protection parties acknowledge the bird strike risk as such and the need to reduce this risk. Although the parties agree on the necessary measures, there is no such consensus with regard to their effect. As a result, there are also differing views as to the (cost-)effective implementation of these measures.
§ Due to the high level of urgency involved, there is no time to wait for the outcome of ongoing pilots to assess alternative control measures that would yield results in the longer term. The reduction of goose populations represents the most effective short-term measure. In the longer term, habitat management and improvement of the measures to detect and scare off birds could also help structurally reduce the risk of bird strikes.
§ Seven civil-society organisations united in the “Goose 7” recently prepared a joint national and regional recommendation, outlining measures to reduce and stabilise the population of various types of geese in the Netherlands at a certain level. The implementation of this recommendation as a short-term measure will require the approval of the State Secretary of Economic Affairs, Agriculture and Innovation, which approval thus far has not been forthcoming.
§ The Ministry of Infrastructure and the Environment, responsible for aviation safety, has not sufficiently coordinated measures aimed at reducing the risk of bird strikes.
Seven Safety Recommendations were made as a result of the Investigation:
§ That Royal Air Maroc demonstrate to the Moroccan Ministry of Transport that:
§ the procedures for communication and crew resource management between crew members have been harmonised with the international standard for airline pilots.
§ pilot training has been expanded to include simulations of multiple unexpected failures.
§ That Air Traffic Control the Netherlands and the Minister of Infrastructure and the Environment:
§ ensure that aircraft in distress flying under the minimum vectoring altitude are informed about high obstacles in the Schiphol Control Zone.
§ That the Minister of Infrastructure and the Environment, responsible for aviation safety:
§ take(s) proactive measures to ensure the minimisation of bird strike risks.
§ with the greatest possible urgency and vigour implement effective measures to reduce and stabilise the population of various goose types in the Netherlands at a certain level in accordance with the “Goose 7” recommendation in order to reduce the risk of bird strikes.
§ Ensure(s) that the interests of aviation safety are safeguarded within the various relevant policy domains, by preparing enforceable emergency measures that allow for intervention if the risk of bird strikes becomes too great.
§ Conduct(s) studies to assess the potential of technical measures to reduce the risk of bird strikes.
The Investigation was completed on 29 November 2011 and the Final Report: Emergency landing after bird strike, B734, Amsterdam Schiphol Airport, 6 June 2010 released.