Niugini F70 at Port Moresby on Feb 20th 2023, loss of cabin pressure

Last Update: September 13, 2024 / 14:58:06 GMT/Zulu time

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Incident Facts

Date of incident
Feb 20, 2023

Classification
Accident

Flight number
PX-188

Aircraft Registration
P2-ANT

Aircraft Type
Fokker 70

ICAO Type Designator
F70

An Air Niugini Fokker 70, registration P2-ANT performing flight PX-188 from Port Moresby to Mount Hagen (Papua New Guinea) with 67 passengers and 4 crew, had been on approach to Mount Hagen but could not land in Mount Hagen due to weather conditions and returned to Port Moresby. The aircraft climbed to FL310 enroute but suffered the loss of cabin pressure. The aircraft performed a relatively normal approach to Port Moresby descending through 10,000 feet about 14 minutes after leaving FL310 and landed on runway 14L about 2:10 hours after departure. 4 passengers sustained serious, 18 passengers minor injuries.

Papua New Guinea's PIC reported they were informed about the occurrence only 2 days later and wrote: "On disembarking the aircraft at Jacksons Airport, a passenger of the occurrence flight alerted Air Niugini Customer Service that a few passengers from the flight were bleedingfrom the ears and nose. On assessing the injured passengers, Air Niugini Customer Service then activated a response plan and had the injured passengers transported to Pacific International Hospital for further medical assessment.It was reported that atotal of 22 persons were injured;7 persons had serious injuries and were admitted, 6 persons were under review, and 9 persons were discharged from the hospital." The AIC is investigating the accident.

On Mar 22nd 2023 PNG's AIC released their preliminary report summarizing the sequence of events:

The co-pilot, occupying the right seat, was pilot flying (PF), and the Pilot in Command (PIC) who was in the left seat was the pilot monitoring (PM).

The flight crew had decided to return to Jacksons after observing that the weather at Mt. Hagen Airport, the planned destination, was not suitable for an approach and landing.

The Flight Data Recorder (FDR) data showed that the aircraft had originally departed from Jacksons Airport at 14:07. The flight crew stated during interview that they arrived overhead Mt. Hagen Airport at 15:00. The flight crew reported that on approach for landing into Mt. Hagen Airport, they elected to maintain 8,000 feet (ft) above mean sea level (AMSL) and visually hold to the West of the Airfield over the Mount Hagen Township, due to the prevailing wind conditions in the circuit. The hold lasted for about eight minutes.

When interviewed, the flight crew stated that, given the local wind conditions observed in the circuit during the hold, a safe landing was not possible, and therefore a decision was made to return to Jacksons Airport. Recorded data showed that the aircraft climbed to a cruising altitude of 31,000 ft AMSL and began tracking back to Jacksons.

About 100 NM3 from Jacksons, the crew commenced their descent. The crew stated that a track deviation of 30 NM right of track was required to keep clear of enroute weather. Approaching 10,000 ft AMSL on descent into Jacksons Airport, the crew actioned the Fokker 70 Normal Procedures Before Approach Check. The flight crew stated during interview that they subsequently noticed that the Landing Elevation Setting4 had not been set for an arrival into Jacksons but was instead, still maintained at about 5,500 ft, which they initially set for Mt. Hagen Airport.

The crew stated in the interview that since there was a need to increase the rate of pressurizing the cabin on descent, the Fokker 70 Quick Reference Handbook (QRH) Abnormal Procedures for Manual Cabin Pressurization Control Procedure was executed, and they continued with the approach for landing into Jacksons Airport via the ILS5 procedure for Runway 14L.

The crew stated that once the aircraft was established on final approach for Runway 14L, the cabin pressure differential indicated about 6 PSI6. Seeing that the indication was above the maximum allowable cabin differential for landing (0.13 PSI), the crew terminated the approach and initiated a Go Around at about 16:00, from 1,000 ft AGL7 straight ahead over Runway 14L.

The aircraft climbed on runway heading to 2,500 ft AGL and requested, for clearance from ATC8 to conduct a right hand turn to track and visually hold at 2,500 ft in the Daugo Training Area (D901). ATC provided the clearance as requested by the crew.

The aircraft established at established at D901 at 16:06. The crew reportedly actioned the QRH Abnormal Procedure for “Reduced Cabin Pressure Differential Procedure”. The aircraft then left the hold at D901 and with ATC clearance, tracked for a right base turn at about 16:14. The crew reportedly conducted a normal approach and landed on Runway 14L at 16:20. The crew taxied to the parking bay where the engines were shut down. The engines were shut down at 17:17.

A normal disembarkation procedure was followed, and all passengers disembarked.

According to customer services duty officer’s statements provided to the AIC, four passengers were reported to have sustained serious injuries and 18 passengers sustained minor injuries. For all crew and the remaining 45 passengers, no injuries were reported.

The injuries were reported to have been sustained during flight operations Jacksons aerodrome area as a result of a sudden pressurization event.

On Sep 13th 2024 the AIC released their final report concluding the probable causes were:

- Organisational factors like multiple changes to flight crew roster and last-minute notification to crew resulted in task saturation and stress, that prevented crew situational awareness and good crew resource management and decision making on the day of the serious incident. This resulted in the oversight by the crew to set Port Moresby landing altitude in Mt. Hagen.

- Operational and environmental conditions impacted the way crew conducted their operation in Mt. Hagen and in Port Moresby.

- The flight crew did not complete the final step of the Fokker 70 Abnormal Procedures Manual Cabin Pressurisation Control, which was to set the Manual control lever to the ‘UP’ position before landing to depressurise the cabin and prevent any further pressurisation. Due to not completing the procedure, the cabin differential began to increase again on finals which led to a go-around. Some passengers and cabin crew sustained injuries during the go-around due to a rapid change in cabin pressure. The flight crew then actioned the Fokker 70 Abnormal Procedures for Reduced Cabin Differential.


The AIC analysed:

The flight crew had only identified the incorrect LAS during the descent into Port Moresby. The LAS was still set to the Mt. Hagen elevation at 5,500 ft instead of being set to sea level for Port Moresby. As a corrective action, the crew made the decision to initiate the Manual Cabin Pressurisation Procedure.

The Manual Cabin Pressurisation Procedure is only to be actioned in the event of a pressurisation issue when there is a fault with the automatic CPC. The AIC found that the execution of the Manual Cabin Pressurisation Procedure was non-standard. Since there was no failure of the cabin pressure controller system in Auto mode, there was no reason to go to Manual mode. With reference to the aircraft Manuals and checklists of the Fokker F70, the Manual mode should only be used in case the AUTO mode fails (for instance the pressure controller), or in case of a cracked windshield to decrease the differential pressure. The action of the flight crew to increase the descent rate of the cabin altitude demonstrated an improper use of the Manual mode. It was also noted that despite there being other options available to the flight crew to allow the CPC to automatically pressurise the cabin to sea level, their decision to initiate the Manual Cabin Pressurisation Procedure was influenced by a combination of factors.

At the time of the serious incident flight, the AIC found that the crew were subjected to time pressure. When the incorrect LAS was discovered, the aircraft was approaching 10,000 ft and the LAS was at 5,500 ft. The aircraft was also descending at a rate of more than 2,000 ft per minute (fpm).

From 10,000 ft it would have taken the aircraft less than 5 minutes to touchdown if the descent was continued at that rate. It was also noted that following the correction of the LAS from 5,500 ft to sea level, at an average rate of 300-400 fpm, the automatic pressure controller would have required at least 11 minutes to pressurise the cabin from 5,500 ft to sea level. If the crew opted to continue the approach at a descent rate of 2,000 fpm while allowing the automatic pressure controller to pressurise the cabin at a rate of 300-400 fpm, the aircraft would have caught the cabin at about 3,000 ft and as a result the cabin would have suddenly depressurised via the Outflow valves, causing discomfort and potentially injuring the passengers.

Due to the time pressure that the crew were subjected to at the time, it was found that the crew decided to continue the approach to landing and at the same time presssurise the cabin from 5,500 ft to sea level with the intention of preventing further delay. The decision was then made to manually pressurise the cabin to sea level at a higher rate.

On the initiation of the Manual Cabin Pressurisation Procedure, the flight crew selected the Manual function, moved the Manual control lever to the down position and increased the rate of cabin pressurisation by adjusting the control knob to a rate of 800-1000 fpm. The cabin continued to pressurise manually at the increased rate as the aircraft continued to descend.

Around this time, the passengers started to experience discomfort. This was a result of the increased rate of pressurisation by the crew from 300-400 fpm to 800-1000 fpm. The aircraft continued to descend and at about 2,500 ft the crew observed the cabin pressure indicating sea level. They subsequently moved the manual control lever from the DOWN position to the MID position. This caused the outflow valve to maintain a static position to hold the cabin pressure at sea level. The crew then actioned the Before Landing Procedure to configure the aircraft for landing.

According to the Quick Reference Handbook, before landing, the manual control lever must be moved to the UP position to prevent any further pressurisation and to remove all residual pressure from the cabin to avoid a sudden depressurisation on touchdown. The AIC found that the manual control lever was not moved to the UP position after the aircraft was configured for landing.

Approaching 1,000 ft on finals, the crew observed the cabin differential indicator value increasing to 3 psi. Since the reading was above the maximum value permitted for landing, the crew initiated a go around. Applying full power significantly increased the rate of compressed bleed airflow to the cabin. However, with the outflow valve maintaining a static position to a pressurisation rate setting of 800-1000 ft, the bleed air inflow rate caused by the application of Go around power, could not be complemented by the outflow valve to maintain the selected cabin descent rate.

The AIC concluded that if the manual control lever had been in the UP position at the time full power was applied, the outflow valve would have been able to move to fully open position providing pressure relief and the cabin pressure would not have risen to an unsafe level. The AIC determined that this pressurisation event resulted in the severe ear and sinus pain and bleeding experienced by the passengers.

Furthermore, in an attempt to reduce the cabin differential, the crew decided to execute the Abnormal Procedure for Reduced Cabin Differential Procedure. The AIC notes that the Reduced Cabin Differential Procedure is used to reduce further damage when a crack in the front window or sliding window is observed. However, on the crew’s execution of this procedure, the AIC noted that the final step of the Reduced Cabin Differential Procedure involved placing the manual control lever on the Cabin Pressure Selector on the overhead panel to the UP position. In both procedures, the execution of this step is to remove any residual pressure from the cabin. Given that the cabin had been pressurised as observed on the increased cabin differential, when the crew executed the final step of the Reduced Cabin Differential Procedure, the aircraft experienced a sudden depressurisation via the outflow valves.

As a result of the sudden depressurisation, a thick cloud of mist was observed in the cabin, similar to that observed on sudden depressurisations at altitude. The aircraft continued with a normal approach and landing.

The AIC established that the CPC was serviceable at the time of the serious incident. Additionally, the Manual Cabin Pressurisation Procedure is not recommended when there are no faults with the automatic function of the CPC. However, the crew decided to use the procedure as an alternative instead of delaying the approach to allow the CPC to automatically pressurise the cabin. Furthermore, the procedure was incorrectly applied by the flight crew resulting in the cabin pressurisation event.

Time Pressure

The operator's Flight Administration Manual outlines the provision for short notice of roster changes to flight crew as required by operational demands. However, the manual does not specify the limitation on time in which flight crew can be notified on short notice of roster changes.

On the day of the occurrence, the flight crew were notified of the change in roster 20 minutes prior to the required sign-on time. Due to the short notice, the flight crew signed on late for duty, and the flight from Port Moresby to Mt Hagen was subsequently delayed by just under an hour.

Given that the flight crew had already been rostered beforehand to conduct an international flight from Port Moresby to Cairns with an estimated departure time of 17:00, and with the predicament of the delayed flight out of Port Moresby for Mt Hagen, the AIC assessed the flight crew's decision-making, actions and inactions inflight and post-flight, and determined that the flight crew was adamant to not cause consequential delay to the departure of the international flight. The AIC determined the flight crew's conduct was done out of time pressure to meet commercial expectations.
It is the view of the AIC that the operator's existing procedures on Crew Rostering imposes, among other risks, time pressure on flight crew, especially in instances where flight crew endeavor to not cause consequential delays to their subsequent rostered flights throughout the day. Although it is understood that the delivery of service determines the profitability of the operator, it is the opinion of the AIC that when flight crew are exposed to operational time pressures, it is highly likely that their decision-making will be heavily influenced by the need to meet commercial requirements to the extent that safety may be compromised, unintentionally, due to human error.

Human Factors

An accident or incident is not solely the result of an action taken by one individual. The potential for an accident is created when failed or absent defenses, human error (intended and unintended actions) and existing conditions present within an organisation or air transportation system interact in a manner which breaches all the defenses that result in an accident or incident. The front-line personnel (Flight crew, Air traffic controller, Cabin crew etc.) are the last line of defense. The investigation identified absent or failed defenses, human error and tasks and environmental conditions that directly or indirectly contributed to the abnormal cabin pressurisation event.

Due to numerous crew roster changes and reallocation of flights on the day of the occurrence, the flight had departed Port Moresby behind schedule. At the time of the occurrence, the existing crew rosters showed no evidence to support a flight and duty related fatigue situation. However, the numerous roster changes on the day of the flight, to flight crew’s daily schedules, posed a likelihood of acute mental stress and fatigue, compounding with the initial tasks of daily flight planning. For crew to be subjected to multiple roster changes on short notice and prior to sign on, it is highly likely that the crew may have carried the mental stress past sign on, into flight planning stages, through to the flight to Mt Hagen and back to Port Moresby. Other stress factors were observed to be due to task overload with limited time available and degrading operating conditions at Mt Hagen Airport, such as tailwinds, displaced threshold and unavailable PAPI lights on Runway 12 which contributed to the reduced situational awareness of the flight crew. The workload pressure of holding over Mt Hagen township due tailwinds and unable to land on Runway 30 with only 15 minutes of holding fuel and running behind schedule was a likely contributory cause to crew not conducting the necessary scan at 10,000 ft on climb from 8,000 ft to 10,000 ft, when diverting from Mt Hagen to Port Moresby.

The crew also missed other scans from cruise to transition level, which would have been an opportunity to check and set the appropriate destination LAS.

With the late sign on by both flight crew, it is likely that the pre-flight preparations prior to the departure of the initial sector from Port Moresby to Mt Hagen would not have been carried out effectively to identify the hazards associated with the flight and plan mitigating or preventative actions to reduce the risk of an accident. Despite obtaining the latest weather information, weather had changed rapidly leading to unanticipated weather conditions, which was the case in Mt Hagen where they experienced a tailwind component and windspeeds not suitable for landing. It is likely that if a proper preflight preparation would have been carried out, the conditions (weather/wind conditions, displaced threshold on Runway 12 and PAPI lights unavailable on Runway 12) at Mt Hagen Airport as well as the aircraft’s total landing weight, would have been taken into consideration and planned accordingly.

On the day of the occurrence, the crew faced poor crew resource management. This was evident during the diversion phase at Mt. Hagen, where a higher than usual workload environment was observed in the cockpit. The flight crew may have been too busy to recognize that they were overloaded with tasks and missed setting the correct landing elevation for Port Moresby in Mt Hagen during the diversion. The scans and checks from climb to transition level, which could have identified the incorrect LAS, were also missed.

Task saturation, operational and commercial pressures (next flight from Port Moresby to Cairns likely to be delayed due to the late departure out of Port Moresby for Mt Hagen) and degrading operating conditions had added stress on the crew. Evidence showed that the flight crew were distracted due to multiple tasks which resulted in the flight crew not monitoring the overall conditions to make appropriate decisions. This was evident in the flight crew’s decision to control the cabin pressurisation when the automatic mode was functional, and the decision to not advice the relevant persons of the serious incident and the injured passengers prior to landing at Port Moresby. The pilot in command was fixated on landing the aircraft to operate their next flight and erred in his rushed decision to control the pressurisation system manually when automatic mode was functional. However, the co-pilot did not challenge this decision.

There was much to do without enough time which led to the crew’s inability to focus on what really mattered. As task saturation increased, the flight crew might have started shutting down, unable to continue performing effectively.
Incident Facts

Date of incident
Feb 20, 2023

Classification
Accident

Flight number
PX-188

Aircraft Registration
P2-ANT

Aircraft Type
Fokker 70

ICAO Type Designator
F70

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