ANA B788 near Tokyo on Jun 1st 2019, loss of cabin pressure

Last Update: November 27, 2020 / 16:00:17 GMT/Zulu time

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Photo of ANA All Nippon Airways JA828A, Boeing 787-8 Dreamliner — ANA All Nippon Airways JA828A, Boeing 787-8 Dreamliner (Photo credit: Support your local Air Museum! (HawkeyeUK) / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jun 1, 2019

Classification
Incident

Cause
Loss of cabin pressure

Airline
ANA All Nippon Airways

Flight number
NH-171

Departure
San Jose, United States

Destination
Tokyo Narita, Japan

Aircraft Registration
JA828A

Aircraft Type
Boeing 787-8 Dreamliner

ICAO Type Designator
B788

An ANA All Nippon Airways Boeing 787-8, registration JA828A performing flight NH-171 from San Jose,CA (USA) to Tokyo Narita (Japan) with 151 passengers and 12 crew, was enroute at FL430 about 300nm northeast of Tokyo Narita when the crew initiated an emergency descent due to the loss of cabin pressure. The aircraft levelled off at FL100 and continued to Tokyo for a safe landing on Narita's runway 16R about 55 minutes after leaving FL430.

Japan's TSB reported the crew received indications both air conditioning systems became inoperative, declared emergency and performed a descent to about 3000 meters. After levelling off at 3000 meters the crew cancelled emergency and continued to Tokyo. An investigation has been opened.

Japan's Ministry of Transport rated the occurrence a serious incident. When the aircraft was enroute at FL430 over the Pacific Ocean one of the air conditioning systems failed, the other system failed a few minutes later.

The occurrence aircraft has not yet returned to service about 105 hours after landing.

On Nov 27th 2020 the JTSB released their final report concluding the probable cause of the serious incident was:

In this serious incident, it is highly probable that both of the two air conditioning systems shut down at the same time because the Left air conditioning system was unable to restart and the normally having been working Right air conditioning system also shut down during the reset of air conditioning systems of the Aircraft after the Left air conditioning system shut down.

It is highly probable that the Left air conditioning system was unable to restart and the normally having been working Right air conditioning system also shut down because the reset of air conditioning systems was performed at high altitude and under environmental conditions where the CACs (Cabin Air Compressors) tend to more sensitive to surge.

The JTSB reported the crew consisted of the Captain (50, ATPL, 13,386 hours total, 2004 hours on type), an augmenting captain (48, ATPL, 10,545 hours total, 1,472 hours on type) and a first officer. At the time of the occurrence the captain was pilot flying occupying the left hand seat, the augmenting captain was pilot monitoring occupying the right hand seat.

The JTSB described the sequence of events:

While flying at FL 430 bound for Narita International Airport, when the Aircraft gradually decelerated the flight speed from M 0.84 to M 0.78 in order to adjust the arriving time at the Airport, EICAS*6 displayed ”PACK L” indicating that the PACK on the left side had become inoperative at 13:56:49. The PIC checked the operating status of the air conditioning systems with the MFDU*7 and found that among Cabin Air Compressors (hereinafter referred to as “CACs”) that compress air from an outside source and deliver the compressed air to the PACK, both of the two CACs (L1 CAC and L2 CAC) for the Left PACK shut down and the air conditioning system on the left side had been inoperative.

After that, at 14:00:17, according to the procedure to be followed when the PACK is inoperative, which is stipulated in the Company’s aircraft operations manual, the PIC attempted to reset the air conditioning systems by pushing its reset switch.

This enabled to restart the air conditioning systems of the Aircraft, but at 14:02:13, EICAS displayed the “PACK L+R” message indicating that both of PACKs had become inoperative. The PIC checked the operating condition of the air conditioning systems with the MFDU and found that all of four CACs (L1 CAC, L2 CAC, R1 CAC and R2 CAC) shut down and the air conditioning systems on both left and right sides had been inoperative.

Therefore, at 14:02:52, the Aircraft started to descend from FL 430, continued to descend while watching the climb rate of cabin altitude.

And then, at 14:08:00, at FL 277, EICAS displayed the “CABIN ALTITUDE” message indicating that the cabin altitude had reached at an altitude of about 10,000 ft, thus the PIC declared an emergency, made an emergency descent until an altitude of about 10,000 ft, continued to fly, and the Aircraft landed at Narita International Airport at 14:56.

At 14:12:55, when the Aircraft reached at an altitude of about 11,300 ft during the emergency descent, the cabin altitude hit the highest, about 11,400 ft.

In the detailed inspection after arrival at Narita International Airport, any damages and others were not found in the airframe structure of the Aircraft.

The serious incident occurred at about 14:02 on June 1, 2019, at FL 430 about 280 nm northeast of Narita International Airport (approximately 38°54'19” N, 144°45'50” E).

The JTSB analysed:

i) Shut-down of Left air conditioning system

When the Aircraft was flying at FL 430, the airflow generated by the CACs was restricted because the Smarter ECS Mode was activated. Therefore, it is probable that the CACs of the Aircraft were working in a state that surging could easily occur.

After that, it is probable that surging avoidance functions of the VD and the AHV of the L1 and L2 CACs reached performance limits due to the flight environment change by a reduction in airspeed and others, resulting in surging in both CACs.

For this reason, the ABV completely opened in order to smooth airflow to pass through the CACs by reducing the CACs downstream load, which permitted the airflow from the CACs to flow not through the ACM but directly to the cabin, but there was no effect from that, as the ACM protection function*9 was not active, the ACM rpm continued to slow down, and the L2 CAC could not be recovered from surging and shut down.

Because the ACM protection function*9 was not active the ACM rpm continued to slow as the ABV opened completely, and after L2 CAC shut downed, the ACM protection function was active and ABV was fully closed, which, however, further worsened airflow to pass through the L1 CAC, and it is probable that the L1 CAC also shut down without recovering from surging.

As a result, it is highly probable that the Left air conditioning system shut down because all the airflow supply to the PACK L stopped.

ii) Reset operation by the flight crew

It is highly probable that according to the Company’s Aircraft Operations Manual the PIC performed a reset of the air conditioning systems at FL 430 after confirming the L1 and L2 CACs shut down and the Left air conditioning system was not working.

On the other hand, the design and manufacturing company of the Aircraft provided instructions issued on April 5, 2019 to inform operators to descend to 35,000 ft or lower before attempting a reset of air conditioning systems since an air conditioning system may not reset at altitudes exceeding 35,000 ft. It is certain that before the serious incident occurred, the Company had obtained this instruction, but the Company did not yet reflect the content in the Aircraft Operations Manual at the time of the serious incident, because the content had been under consideration in the Company, and this information had not been made known to their flight crews.

iii) Left air conditioning system not recovered by reset

It is probable that at FL 430, the L1 and L2 CACs were restarted, but they were not able to generate enough airflow because of the high altitude exceeding 35,000 ft or higher where the environmental conditions were harsh.

For this reason, it is probable that the ABV completely opened in order to smooth airflow across the CACs by reducing the CACs downstream load, but there was no sustained system effect. The L1 CAC shut down again because the CAC outlet temperature exceeded the limit value and the L2 CAC was not recovered due to a detected surge condition.

As a result, it is highly probable that the Left air conditioning system shut down again because all the airflow supply to the PACK L stopped.

iv) Shut-down of Right air conditioning system

During the reset of air conditioning systems, the function controlling the airflow generated by normally operating R1 and R2 CACs worked to prevent the total airflow of the Left and Right air conditioning systems from surging; it is probable, however, that this allowed those CACs to be easily surging and the surging avoidance functions of the VD and the AHV reached performance limits, resulting in both CACs surging.

After that, it is probable that the R1 and R2 CACs shut down one after another in the same phenomenon as the L1 and L2 CACs described in 3.4 (1) i).

Consequently, it is highly probable that both of the two air conditioning systems shut down at the same time because all the airflow supply to the PACK R stopped and the Right air conditioning system shut down.