On 21 June 2018, an Airbus 220-300 (YL-CSC) being operated by Air Baltic on a scheduled international passenger flight from Geneva to Riga as BTI7QX left the runway soon after touchdown at destination in normal day visibility from its third approach. It then regained the runway but stopped when deflation of a nose landing gear tyre and damage to runway edge lighting were initially suspected and then confirmed. The aircraft was eventually shut down and towed in to its allocated stand for passenger disembarkation.
The start of a Serious Incident Investigation was delayed for in excess of a month. The aircraft operator did not notify the occurrence to the designated State Safety Investigation Agency, the Latvian Transport Accident & Incident Investigation Bureau (TAIIB) without delay as required. The Board only became aware of it when they received a copy of the report of the aircraft operator’s internal investigation dated 22 July 2018. A report of the event occurring was submitted to the Latvian CAA the day after it occurred but they did not notify the TAIIB. However, a copy of relevant FDR data was made available and relevant airport/air traffic operational information was also still accessible.
The 38 year-old Captain, who was PF for the investigated flight, had total of 6,977 hours flying experience of which 929 hours was on type. The extent to which experience had been in command was not recorded. The 29 year old First Officer had total of 2,482 hours flying experience of which 918 hours was on type
It was reported by the crew that an initial ILS approach to runway 18 at destination was broken off because the weather radar was showing a thunderstorm cell on the extended runway centreline at approximately 6 nm. Whilst the flight was being radar vectored to FL70, the aircraft behind continued to a landing and advised that “it’s only rain”.
The flight was positioned for a second approach and followed a Ryanair 737 which went around because of “unstable approach conditions”. At approximately 1300 feet the TWR gave a spot wind of 300° at 14 knots gusting to 30 knots. Because this gust maximum represented a 16 knot tailwind component, a second go around was flown.
Having confirmed fuel remaining would allow a third approach to be attempted and been advised by the TWR controller that the aircraft ahead had continued to a normal landing, the flight was positioned back onto final and this time was given a spot wind of 290° at 12 knots gusting to 17 knots and cleared to land. Two minutes later, another wind check was given of 280° 14 knot gusting to 27 knots. During the subsequent landing flare, the Captain stated that the wind was “strong and gusty” and that “at touchdown they felt like they could not keep the aircraft on the centreline” and it “was veering left and clipped one of the runway edge lights”. After this, an indication of tyre low pressure was annunciated and when checked on the EICAS the left nosewheel tyre was showing as the one affected. The aircraft exited the runway onto taxiway ‘B’ as instructed and then stopped and the crew made a non specific request to ATC to “check the runway”. When asked why an inspection was required, the response was “we nearly ran off the left side of the runway”. The flight was then transferred to GND and a ‘follow me’ vehicle was requested to come and check for a possible burst tyre. This was arranged and GND subsequently advised that no obvious deflation was visually evident but the driver was going to get company engineering to attend. When they did, the deflated nosewheel tyre was confirmed and after the engines had been shut down, the aircraft was towed to its parking stand for passenger disembarkation where it arrived about 40 minutes after landing. By this time, ATC had advised the crew that damaged left side runway edge lighting had been found.
The left wheel marking showing off runway tracking during the runway 17 landing (looking along runway 35). [Reproduced from the Official Report]
The following day it could be seen that the aircraft had actually veered off the runway before being steered back onto it as speed reduced. Accidental activation of the TOGA mode during the final approach was found to have occurred and which resulted in an immediate AP disconnect and loss of selected flight modes and FD guidance.
After touchdown (at about 1.7g) with all wheels on the ground at approximately the same time (within 0.2 seconds), inappropriate flight control inputs then caused the aircraft to veer left and caused an unexpected side load. These consisted of “application of right rudder and a simultaneous increase in left brake pedal pressure". This higher left side brake force caused the aircraft to go left and led to a subsequent aircraft side skid.
This skidding caused excessive sidewall loading to the left nose gear wheel tyre which led to detachment of the tyre inner liner from the wheel rim and complete loss of pressure. When brake force on left brake pedal was reduced, directional control of aircraft was regained. Brake pedal application showed a difference between left and right pedal of up to about 50% with the maximum left brake pedal application recorded at about 95% whilst the right pedal application stayed at about 40%.
The failure of the aircraft operator to report the occurrence was itself investigated. An examination of the OM and other procedural documentation found no reference to the requirement to promptly report Accidents and Serious Incidents to the TAIIB and also no clear responsibility to ensure that aircraft flight recorder data is secured after a notifiable event. The overarching EU regulations in both matters appeared not to have been followed Air Baltic.
The Root Cause of the Serious Incident was determined as “uncoordinated asymmetric flight control inputs by the crew during landing”.
The Direct Cause of the Serious Incident was determined as “force applied to the wheels of the left main landing gear which caused the aircraft to deviate to the left with a subsequent aircraft side skid”.
Possible Contributing Factors were identified as:
- Adverse weather conditions (Thunderstorm)
- Accumulated and increasing level of pilot stress during repeated approaches before the final one.
Two Safety Recommendations were made based on the findings of the Investigation as follows:
- that Air Baltic develop and implement in their Operational documentation procedures for immediate notification of the State Safety Investigation Authority about any Serious Incident or Accident. [LV2019-001]
- that Air Baltic develop and implement in their Operational documentation procedures about cooperation with the State Safety Investigation Authority for removal of aircraft recorders, sampling and access to other evidence in case of a Serious Incident or Accident.
The Final Report was completed on 17 October 2019.