Disaster averted; work to be done (CS-TNV incident Copenhagen)
Credit to website avherald.com and its owner Simon Hradecky
On April 9th, 2022 an A320 approached Copenhagen Airport for a landing from a flight from Lisbon.
The crew decided to go around just before touchdown and had trouble controlling the aircraft; the aircraft veered to the left and lost airspeed to a dangerously low value and the airport perimeter fence was just cleared and the aircraft flew over residential area at an estimated 300 feet.
Eventually the crew was able to get the aircraft under control and gain sufficient airspeed for controlled flight.
After shutting down the left (LH) engine in flight, the crew brought the aircraft in for a safe landing.
During rollout it became clear to spectators that the LH thrust reverser remained deployed partially.
Below the text from Avherald.com (the go to website for global aviation safety incidents)
"A TAP Air Portugal Airbus A320-200, registration CS-TNV performing flight TP-754 from Lisbon (Portugal) to Copenhagen (Denmark) with 102 passengers and 7 crew, was landing on Copenhagen's runway 30 at about 12:05L (10:05Z), when according to ADS-B data transmitted by the aircraft the aircraft veered to the left, the speed over ground reduced sharply from about 133 to about 120 knots, the crew initiated a go around, the aircraft however did not climb but also did not build up speed. With the airport perimeter and houses of the Maglebylille community in the way the aircraft began to slowly climb and crossed the first houses at around 300 feet AGL, the speed over ground further reduced to 101 knots. Once the aircraft had climbed to about 900 feet AGL (1700 feet MSL according to standard pressure 1013 hPa, deduct 800 feet from all transponder altitude readings to get to AGL according to QNH 986 hPa) airspeed began to build up again. The aircraft levelled off at 3000 feet MSL and thereafter accelerated to normal speeds. The aircraft subsequently positioned for another approach to runway 22L and landed without further incident about 20 minutes after the go around."
The event is under investigation by the Danish accident investigation board "Havarikommissionen". Press release downloadable below.
From the report it appears that the aircraft had not touched down during the go-around.
It is also remarked that three of the four thrust reverser doors were found open instead of all four.
This indicates that pilot error is not a contributing factor to the incident; in fact crew action prevented disaster of an aircraft that was operating out of its certification limits due to a technical defect as we will try to show later on.
A large aircraft is not supposed nor requited to be controllable with one engine operating normally and another in reverse thrust configuration. Refer to CS 25.147, downloadable below.
The A320 thrust reverser system structural layout indicated below:
The A320 thrust reverser system has a number of inhibit logic parameters as shown below;
"Thrust reverser deploy sequence
Deploy sequence is only allowed on ground after actuation of the throttle control lever and requires actuation
. One ECU channel operating with its associated throttle reverse signal.
. SOV opening through the SEC and the static relay.
. Main gear compressed signal from at least one LGCIU.
. Throttle lever angle (TLA) reverse signal from at least one second.
Before the transit completion, the ECU sets the reverse idle thrust."
Clearly one of the inhibit parameters were breached.
This could have multiple causes; among which:
Incomplete (de)activation procedure carried out previously
Incomplete installation procedure allowing the reversers (pivoting doors) to unlock.
System failure at some point
There is much to investigate with respect to;
Trying to replicate the failure in order to determine the prevailing conditions
Maintenance conducted in these components previously
Maintenance records reviews
Interviews of maintenance personnel involved in previous maintenance
Condition of all system components
Review of the Digital Flight Data Recorder parameters
Interviews with the crew
Most likely this will result in service and regulatory action such as Service Information Letters os Service Bulletins and/or an Airworthiness Directive