ANTALYA- Russian investigators have provided a detailed account of the extensive damage sustained by a Nordwind (N4) Airbus A321 during a hard landing in Antalya.
After the aircraft’s nose pitched downward just before landing on runway 36C, striking the runway with its nose gear first, the ACARS communications system recorded more than 100 system failures.
Nordwind A321 Go-Around Failures
This included the failure of two inertial reference systems (IRS) and one flight augmentation computer, resulting in the loss of critical flight information such as heading, pitch, roll, and speed on the captain’s side.
This likely occurred due to damage to the air-data reference units in the avionics bay caused by the nose-gear impact.
Although a third IRS, providing data to the first officer’s side, was still functional, it experienced a significant pitch deviation at the moment of impact, remaining 3 degrees out of alignment with the standby instrument’s data.
If two inertial reference systems (IRSs) fail, the aircraft typically transitions to ‘alternate’ law, as the elevator aileron computer cannot perform calculations for ‘normal’ law.
However, the investigation revealed that the aircraft instead shifted to ‘direct’ flight-control law, and the flight-director command bars were deactivated.
Normally, transitioning to an ‘alternate’ law with the landing gear down would lead to a switch to a ‘direct’ law. However, the impact on the nose gear had triggered a false gear-up signal due to sensor damage, causing the change to ‘direct’ law.
This switch was actually prompted by the elevator aileron computer’s assessment that the remaining functional IRS was unreliable following a vertical load check, leading to the rejection of all three IRSs.
As the flight crew advanced the thrust levers to initiate a go-around and the aircraft began to climb, the landing gear remained extended. The pilots reported that the gear lever had jammed.
The investigation noted that while the pitot-static and angle-of-attack sensors on the nose were undamaged, the “significant wrinkling” of the fuselage skin in the vicinity could have potentially impacted their accuracy.
More Issues
While climbing, the flight crew received a smoke alert in the avionics bay, leading them to don oxygen masks. However, the investigation suggests that the smoke detector had been triggered by mist from a hydraulic fluid leak rather than an actual fire.
Airbus A321 aircraft typically have three hydraulic circuits—yellow, green, and blue—operating at a standard pressure of 3,000 psi. Pressure in the yellow circuit dropped to 1,270 psi, triggering an alarm, while the green circuit’s pressure decreased to 2,100 psi.
Pressure fluctuations caused certain hydraulically-powered systems to switch between operational and non-operational states intermittently.
The remaining functioning IRS failed while the aircraft was flying level at an altitude of 3,450 feet, likely due to distorted navigation calculations stemming from the dislodgment of the air-data reference unit. This resulted in the disappearance of attitude and speed references from the first officer’s displays.
In response, the captain, relying on visual guidance and the standby instruments, decided to conduct a low pass over the airport for a closer inspection of the landing gear.
Hydraulic Failures
Approximately 90 seconds after this decision, the yellow hydraulic system experienced a sudden loss of pressure and ultimately failed. The cessation of fluid spray from the failed system and the crew’s actions to ventilate the aircraft led to the smoke warning ceasing.
However, due to the failure of the yellow hydraulic circuit and insufficient pressure in the green circuit, the flaps remained in their 30° setting even after the crew attempted to select full flap deployment. The slats, which relied on the blue hydraulic circuit, did extend as intended.
During the low pass over the airport, it was confirmed that both the nose gear and main landing gear were extended, and the crew prepared for a second approach.
Further hydraulic issues arose when the green circuit’s reservoir began to overheat. Differential pressure between the yellow and green circuits caused the aircraft’s power-transfer unit to operate continuously instead of being inhibited by a nose-gear signal, which was absent due to damage sustained during the nose-gear impact.
The investigation noted two brief “jumps” in yellow circuit pressure that allowed for the full extension of the flaps, albeit momentarily.
Subsequently, the yellow circuit pressure dropped to zero, followed by a similar pressure loss in the green circuit a few seconds later when the first officer deactivated the green hydraulic pump in response to the overheating warning.
The loss of the green circuit resulted in the unavailability of several systems, prompting the crew to declare an emergency.
100+ Failures
Investigators have reported that ACARS documented a total of 103 system failures following the runway impact.
During the approach, the crew executed it in ‘direct’ law, which offered limited control over the configuration and horizontal stabilizer, with most of the spoilers being unavailable and unable to engage reverse thrust.
Despite experiencing deviations from the glideslope, the twinjet successfully landed at a speed of 125 knots, experiencing a 1.23g impact before coming to a stop on the runway. Fortunately, none of the seven crew members, the aircraft’s sole occupants, sustained any injuries.
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