Delta B763 over Atlantic on Feb 8th 2022, cabin pressure problems

Last Update: December 11, 2023 / 17:43:28 GMT/Zulu time

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Incident Facts

Date of incident
Feb 8, 2022

Classification
Incident

Cause
Cabin pressure problems

Airline
Delta Airlines

Flight number
DL-126

Departure
New York JFK, United States

Destination
Madrid, Spain

Aircraft Registration
N1602

Aircraft Type
Boeing 767-300

ICAO Type Designator
B763

A Delta Airlines Boeing 767-300, registration N1602 performing flight DL-126 (dep Feb 7th) from New York JFK,NY (USA) to Madrid,SP (Spain) with 59 passengers and 9 crew, was enroute at FL350 about two hours into the flight when the automatic cabin pressure control indicated a failure. The crew subsequently controlled the cabin pressure manually. After reaching Spain at FL370 the cabin depressurized prompting the crew to don their oxygen masks, the passenger oxygen masks were released, and initiate an emergency descent to FL120. The aircraft subsequently climbed back to FL280. The aircraft landed in Madrid without further incident about 55 minutes after leaving FL370 and about 6.5 hours after departure from New York.

On Feb 22nd 2022 Spain's CIAIAC reported an investigation was opened into the occurrence.

On Dec 11th 2023 the CIAIAC released their final report concluding the probable causes of the incident were:

The investigation has revealed that the incident was caused by water leaking from a tube with a broken clamp which, when it froze, blocked the outflow valve doors.

The following factors are thought to have contributed:

- The use of plastic tube clamps in the vicinity of the OFV (section 46), the deterioration of which had previously caused leaks in other incidents in the avionics compartment (section 41), where they had since been replaced by metal clamps.

- The absence of a fault in the BITE ground test performed prior to the flight.

- The fact that there is no requirement to perform a visual inspection of the OFV during Task 803 of 21-31 of the FIM when the automatic pressurisation system becomes inoperative in flight, the manual operation is normal, and the BITE does not detect a fault on the ground.

The CIAIAC analysed:

Analysis of the leak

Following the incident, the operator’s maintenance personnel detected a water leak under the rear galley on the left side of the aircraft at station 1562, coming from a tube (PN 79211-012) secured with a broken plastic clamp (CA62507-56BL).

On the flight from Barcelona to New York, the water leak could have caused water to accumulate and ice to form, blocking the movement of the OFV and rendering the automatic pressurisation control system inoperative. The crew managed to control the cabin pressure manually, so the manual mode motor (DC motor) was able to move the OFV and overcome the ice blockage.

Subsequently, during the incident flight from New York to Madrid, the water leak could have once again caused ice to form, blocking the movement of the OFV and rendering the automatic pressurisation control system inoperative, with the situation being further aggravated when the manual control was also unable to overcome the OFV’s ice blockage.

Analysis of the use of plastic clamps

Service Bulletin 767-38A0073 identified the potential for a ruptured plastic clamp to cause a water leak that could affect the electronic equipment in the forward section of the aircraft.

Despite the fact that the IPC provides one-way interchangeability from the plastic CA625 series to the metal 14C33 series, there are no publications explicitly addressing the need to implement said change in section in which the OFV is located.

As the OFV is an electromechanical device, using metal clamps in its vicinity could have mitigated the consequences of a water leak caused by a broken clamp and a subsequent OFV blockage.

The recording of another incident by the operator two days later, in which a broken plastic clamp led to the formation of ice on the OFV and the failure of the automatic in-flight pressurisation system, confirms the need for metal clamps to be used.

Analysis of the detection and recording of the fault in the CPC memory

According to the information provided by the CPC manufacturer, if an OFV blockage resulted in a temporary loss of control of the OFV, the in-flight BITE test would have detected and recorded the AC MOTOR fault in the memory.

According to the information received, on the ground, both the BITE test performed by the operator before the start of the incident flight, triggered by the CABIN AUTO INOP warning from the previous flight, and the test performed after the incident, did not find a fault.

The system had detected the failure in flight, but it could not subsequently recover it on the ground. This could be due to the fact that the fault was not recorded or that the BITE ground test was not executed as indicated in the task. The BITE test checks the system’s integrity, but on these two occasions, the OFV blockage fault could not be recovered once on the ground. Consequently, we have concluded that the CPC manufacturer should assess the possibility that the system may be failing to record faults and consider the consequences because if the fault (AC MOTOR) had been recorded as expected, task 803 of sections 21-31 of the FIM would have indicated the need to replace the OFV actuator as a first step in attempting to isolate the fault and, therefore, would probably have resulted in the water being identified earlier. Also, given the possibility that the test may not have been executed as the task indicates, we believe it necessary for the operator to disseminate the lessons learned from this incident to the maintenance technicians.

Analysis of task 803 of 21-31 of the FIM

Before the incident flight, given the simultaneous failure of two independent pressure control systems with the manual system operating normally and a BITE test with no recorded failures, the possibility that the other common system components, including the OFV, may have failed, could have been considered despite the fact that running task 803 of the FIM through the BITE test determined that the system was okay.

Therefore, in the event of the automatic pressure control system becoming inoperative due to the failure of both the independent control systems but with the manual control functioning correctly, we believe the FIM should recommend additional inspections that would have identified the presence of water before the incident flight, such as a visual inspection of the OFV.

Analysis of the position of the OFV and the location of the ice

The graphs in Figure 23 show that following the failure of the automatic pressure control on the incident flight, the cabin pressure dropped and rose, signalling the active manual control by the crew. Therefore, the OFV was responding to the movements commanded by the crew. From 06:17:04 h, the pressure started to decrease until it reached 10 psi at 06:24:44 h. Consequently, we can determine that this is the period in which the OFV was blocked, leading to depressurisation. It is believed that the water froze in the control arm or the OFV actuator linkage, preventing the motors from closing the OFV.

Analysis of the management of the depressurisation

During the period that followed the activation of the CABIN ALTITUDE warning indicating that 10000 ft of cabin altitude had been exceeded, all the occupants (passengers and crew) used their oxygen masks, and the aircraft descended to a safe altitude.

Both pilots’ statements indicate that they performed the memory items associated with the CABIN ALTITUDE warning. According to the procedure, the actions required to commence the emergency descent manoeuvre after checking the cabin altitude and rate should have been performed without delay; however, despite having lost control of the pressurisation, they were not taken until six minutes after the warning activated, during which time the cabin altitude rose to 18400 ft, possibly because of the focus on regaining control.

According to the logic that automatically deploys the cabin oxygen masks and the in-cabin pressure data recorded on the FDR, they should have been deployed when the aircraft was near FL340. Despite not making the emergency descent to Vmo as per the CABIN ALTITUDE procedure, the aircraft reached FL120 approximately seven minutes later and within the capacity of the oxygen generators, during which time the passengers and cabin crew were supplied with oxygen through the masks.

On seeing the oxygen masks being deployed, the line training captain in the passenger cabin went to the flight deck and took the co-pilot’s seat. Although he thought the best decision was to exchange positions, in this situation and based on the information gathered during the investigation, there did not appear to be any circumstances in which swapping seats with the qualified, experienced and non-incapacitated co-pilot would assist in regaining control over the pressurisation and completing the emergency descent manoeuvre. For the duration of this exchange, only one pilot (the captain under supervision) remained in a cockpit seat with the oxygen mask in place and in charge of continuing the emergency descent manoeuvre.

This situation could have been avoided if the line training captain had occupied the jump seat using the oxygen mask and assisting the other two pilots through the emergency in the few short minutes that remained to reach a safe altitude.

The lack of a CVR recording covering the period of the incident limited the analysis of the events.

The cabin crew had extensive experience and were completing the breakfast service. They reported during their interviews that they responded to the loss of pressure by taking the actions described in paragraph 1.6.8, ensuring the welfare of the passengers.

On reaching the safety altitude, the line training captain informed the purser and explained what had happened to the passengers. During their interviews, the cabin crew explained that the information provided to the passengers by the line training captain reassured and comforted them.

Analysis of the continuation of the flight

The flight crew decided to continue to their destination airport in Madrid, from which they were approximately 250 NM away in favourable weather conditions. Having regained control of the pressurisation, they decided to climb, being cleared to FL280.

According to their account, they based this decision on optimising the remaining fuel and even considered flying at a higher altitude for better terrain clearance despite ATC informing them of the minimum altitude they could descend to.

During the prior emergency descent, the oxygen generators that supply the masks in the passenger cabin had been activated, the duration of which was limited. It should be noted that there were 59 passengers on board, i.e. approximately one-quarter of the passenger seats were occupied. During the loss of cabin pressure, the oxygen generators corresponding to these 59 seats were activated. The crew did not recall any coordination measures being taken in this regard.

On the other hand, the automatic pressurisation system had failed on two consecutive flights, and on this occasion, the manual control had also failed temporarily, which was indicative of some kind of anomaly in the pressurisation system and, therefore, a recurrence of the failure for the remainder of the flight could not be ruled out.

Furthermore, taking into account the fact that the crew have recently undergone refresher training on the pressurisation system, the issue of a safety recommendation to the operator to reinforce crew training related to cabin pressure loss and to include the lessons learned from this event is considered appropriate.
Aircraft Registration Data
Registration mark
N1602
Country of Registration
United States
Date of Registration
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Manufacturer
BOEING
Aircraft Model / Type
767-332
Number of Seats
Qff Subscribe to unlock
ICAO Aircraft Type
B763
Year of Manufacture
Bpbi Subscribe to unlock
Serial Number
Ckpfm Subscribe to unlock
Aircraft Address / Mode S Code (HEX)
QhkAjk Subscribe to unlock
Engine Count
E Subscribe to unlock
Engine Manufacturer
Ek Subscribe to unlock
Engine Model
Qqbeih h kcf Subscribe to unlock
Engine Type
Lfkkgfjde Subscribe to unlock
Pounds of Thrust
N jif Subscribe to unlock
Main Owner
Fm gmAnmgpcekdepfngjjqinpqgepdciAcmg eAiejhpcdlgdicpjjkhlAehdbAqefm ccclnhfcb hhbhnjfenmmnmkhAnhemnliiehAidikccimffnp Subscribe to unlock
Incident Facts

Date of incident
Feb 8, 2022

Classification
Incident

Cause
Cabin pressure problems

Airline
Delta Airlines

Flight number
DL-126

Departure
New York JFK, United States

Destination
Madrid, Spain

Aircraft Registration
N1602

Aircraft Type
Boeing 767-300

ICAO Type Designator
B763

This article is published under license from Avherald.com. © of text by Avherald.com.
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