Description 

On 21 November 2019, a Boeing 737-800 (TC-JGZ) being operated by Turkish Airlines on an international passenger flight from Istanbul Ataturk to Odesa as TK467 and making a second ILS approach to runway 16 at destination in night VMC left the side of the runway soon after touchdown before regaining after 550 metres with the nose and right main landing gear legs collapsed and coming to a stop. An emergency evacuation was completed with no injuries to the 142 occupants but the aircraft sustained significant FOD ingestion damage to both engines, damage to the left engine cowling and lower fuselage as well as to the landing gear. 

Investigation

An Investigation into the Accident was carried out by the Ukraine National Bureau of Air Accident Investigations (NBAAI). All relevant data was recovered from both the FDR and two hour CVR with the assistance of the Turkish Transport Safety Investigation Centre due to a lack of any data readout equipment at the NBAAI.

The 42 year-old Captain, who was acting as PF for the accident flight had a total of 6,094 hours flying experience of which 5,608 hours were on type including significant time in command. He had operated to Odesa once previously, about a year before the event. The 31 year-old First Officer had a total of 252 hours flying experience of which 77 hours were on type and had not previously operated to Odesa. 

What Happened

According to the Captain, the flight crew had been fully aware of the potential weather issues in relation to variable wind velocity at Odesa during the pre flight briefing. He noted that the crosswind component was close to the limit. However no other operational constraints in relation to landing were identified. As a precaution, sufficient fuel was uplifted to allow Istanbul to be used as an alternate in the event that a landing at Odesa was not possible.

During descent, having listened to the latest ATIS, which was not significantly different from earlier reports and the forecast, the Captain decided that the flight could continue as planned with the expectation of an ILS approach to runway 16. The ATIS wind represented a crosswind component for landing which was within the applicable 30 knot limit but the tailwind component was potentially around the 15 knot limit based on conversion of the given values in metres per second. The Captain briefed the First Officer to “monitor the value of the cross wind component using the FMC progress page” during final approach but made no mention of the significant tailwind component. He also warned the First Officer about the significant (the CVR recorded him mentioning 90%) chance of a go around being necessary because of the potential consequences of the variable wind velocity conditions. On listening to a subsequent ATIS, little change was apparent. The runway continued to be reported as “dry”.

Initial positioning was via the OGLAR 3Y SID followed by radar vectoring to the runway 16 LOC. Transfer to TWR was followed by a landing clearance and spot (2 minute average) wind check but there was no additional reminder of the still variable wind direction. The approach was initially stabilised and further (similar) wind checks were provided and all, as given, were “within permissible values” but without any reference to the variable wind direction. Forty seconds after a final wind check, a go around was commenced with the crew subsequently advising that the approach had become unstabilised. FDR data subsequently showed that the applicable 153KIAS VREF had been exceeded by 18 knots.  

A climb to 3000 feet QNH was followed by radar vectoring for another ILS approach to Runway 16. A new ATIS was copied which was little different to the previous ones. A direct request to ATC for the latest (spot) surface winds was made and those given (in metres per second) were potentially marginally above the 30 knot crosswind limit and as a result, the Captain decided on further holding. A climb to 8000 feet was commenced due to icing at 3000 feet. 

Sixteen minutes after beginning the go around, the controller gave the flight updated wind information, this being the only time figures for the extent of the variable wind direction were included. The figures given (with speed converted to knots) were 070º/17 gusting to 25 knots direction varying between 050º and 110º and on hearing this, the flight advised ready for another approach. The subsequent approach was stabilised at 1000 feet aal and remained so thereafter. Straight after the automated ‘minimums’ call, the Captain was recorded on the CVR confirming his intention to land.

The right main landing gear touched first at 444 metres beyond the threshold of the 2,800 metre long runway slightly left of the runway centreline, the left main gear followed almost immediately and the nose landing gear touched down 552 metres beyond the  threshold and 1.5 metres to the left of the centreline. The spoilers were automatically deployed and reverse thrust was selected. A modest right rudder input aimed at correcting the increasingly left of centreline track (4° to the left of the direction of the runway centreline) was made but had no effect and three seconds after deploying reverse thrust, FDR data showed that, with the speed still a 130 knots, the Captain had used the steering tiller to suddenly turn the nose landing gear to the right through a recorded 78º. As subsequently confirmed from rubber marks on the runway, this action led to a skid of the nosewheels which had no corrective effect on the trajectory of the aircraft and caused the tyres to begin to disintegrate.

At a speed of 111 knots, the nose landing gear departed the left side of the 56 metre-wide runway into soil with the rudder deflected to just over half the maximum possible deflection to the right. Shortly after this, the nose landing gear collapsed rearwards and over the next 23 seconds, as the ground speed decreased from 107 knots to 2 knots, the right main gear also collapsed. After a distance of 550 metres to the left of the runway (see the ground track on the illustration below) which was mostly parallel to the runway edge, the aircraft re-entered the runway just after its intersection with the second runway access taxiway before coming to a stop 1,683 metres beyond the runway threshold and 27 metres left of the centreline.

Why It Happened

It was noted that the FCTM provides three techniques for landing in strong crosswinds on a dry runway. However, FDR data indicated that the touchdown was made without fully aligning the aircraft with the runway centreline which was explicitly not recommended when landing on dry runways in the presence of strong crosswinds. In the flare, it was also noted that there had also been insufficient into-wind aileron to keep the wings level.
 

The ground track of the aircraft before, during and after the runway excursion. [Reproduced from the Official Report]

Once the nose landing gear was on the ground, it became difficult to turn the aircraft to the right given the combined effect of the crosswind component, the force of reverse thrust and insufficient rudder deflection angle. The Captains’ decision to make a sudden large input on the nose wheel steering tiller - up to a recorded 78º - when this system is only intended for use at low speed guaranteed that a skid would begin in the existing direction of deviation.

In respect of TWR communicating to the crew the full extent of variations in surface wind velocity, it was considered significant that little attempt was made to pass useful data on the extremes of wind direction when giving wind speed variation given the display available. 

The Investigation concluded that the Cause of the runway excursion accident was “failure to maintain the direction of the aircraft movement during the landing roll in a strong and variable crosswind”.

Four Contributory Factors were also identified as follows:

• the use by the flight crew of the “crab” touchdown technique which is not recommended in the aircraft manufacturer’s FCTM on a dry runway in strong crosswind conditions 
• insufficient action taken by the flight crew to align with and maintain the runway centreline.
• the presence of a significant crosswind component
• the effect of a wind direction which varied between crosswind/tailwind and crosswind/headwind components during the landing roll  

A total of 15 Safety Recommendations were made as a result of the Investigation some of which were in respect of other incidental findings which had no directly causal effect on the excursion: 

• that the Odesa International Airport Operator conduct additional inspections of the pavements surfaces and document any deterioration of their condition in cases of takeoff and landing use by overloaded aircraft and if required stop flights and perform necessary repairs in case of the detection of new defects (such as cracks, chipped edges and panel corners, subsidence, etc.) which may cause unacceptable damage to the integrity of the pavement and pose a threat to flight safety.
• that the Odesa International Airport Operator provide aircraft operators which perform flights to Odesa with up-to-date information on operating restrictions in terms of traffic intensity and aircraft weight.
• that the Odesa International Airport Operator monitors a sample of takeoff and landing events each day and follows the recommendations of the scientific-research organisations that conduct relevant studies of aerodrome pavement status in relation to use.
• that the Odesa International Airport Operator bring the instruction on TWR controllers’ use of Remote Lighting Control Equipment as  approved by the Airport’s General Director on 12 May 2011 into conformity with the current aviation legislation of Ukraine.
• that the Odesa International Airport Operator ensure that voice communications through direct communication and radio exchange channels during emergency and rescue operations using the live monitoring and recording system are recorded in accordance with paragraph 4.11 of the Regulations of Emergency Rescue and Fire Safety Support of Flights.
• that the Odesa International Airport Operator establish the frequency of assessment of braking action characteristics on the runway surface according to paragraph GM1 ADR.OPS.C.010(b)(3) (c) of the Acceptable Means of Compliance (AMC) and Guidance Material (GM) which clarify the provisions of the “Technical Requirements and Administrative Procedures for Certification of Aerodromes" under the Aviation Regulations of Ukraine.
• that the Ukrainian State Air Traffic Services Enterprise (UkSATSE) should ensure that during radio exchanges, ATS controllers provide flight crews with information on significant variation in the wind direction, not just its averaged values so as to comply with the requirements of Instruction No. 01 (i) dated 11 January 2018 on Meteorological Service of Aircraft Flights at Odesa Aerodrome.
• that the Ukrainian State Air Traffic Services Enterprise (UkSATSE) supplement the Operating Instructions of the ATS control units with clear requirements for providing crews with information on significant wind direction changes, for example, of the following content: “During the aerodrome control/ approach control service, upon a crew's request, an ATC controller shall transmit to the crew an average direction and speed of the surface winds, including their significant changes, regardless of whether the crew has previously listened to this information.”
• that Ukraine Aircraft Operators jointly with Ukraine Aerodrome Operators analyse in advance the compatibility of an aerodrome with the operation particular aircraft types according to the recommendations set out in Chapter 4 of ICAO Doc 9981 ‘Procedures for Air Navigation Services - Aerodromes’, namely assess the
• compliance of the aircraft type as flown with the aerodrome infrastructure to ensure that aircraft using an aerodrome are compatible with the aerodrome certification status.  
• that Turkish Airlines:
  • Conduct theoretical training of aircraft flight crews in choosing a type of landing on dry runways at limit values of the cross component of the wind.
  • Introduce into the simulator-based training program, as regards landing with the maximum permissible crosswind, the following:
    • taking decision on landing in the conditions of the maximum crosswind and tailwind of variable directions
    • correctness of choice of landing approach method versus runway status and crosswind strength
    • timely and effective actions to maintain the landing run direction
    • specific features of the reverse thrust application
  • Consider the positive and negative aspects of the three types of touchdown on a dry runway which are recommended by the FCTM
  • Supplement the airline's guidance documents with the requirements obliging aircraft crews to discuss during the approach briefing the specific features of the landing performance depending on the conditions at the aerodrome.
• that the State Aviation Administration of Ukraine, take into account during inspections of the ground aids for radio technical flight support at the aerodromes of Ukraine, the requirements set out in the regulation on their operation, as provided by the manufacturer of such means.
• that the National Bureau of Air Accident Investigations (NBAAI) provide the relevant NBAAI units with FDR/CVR read-out devices.

The Final Report was published on 19 November 2020.

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