Cessna Citation Exhaust Nearly Shot Down Vueling Airbus A320
The final report of the French Bureau of Investigation and Analysis for Civil Aviation Safety (BEA) examined how a crew of a Vueling Airlines Airbus A320 was partially incapacitated during a flight of routine from Geneva Airport (GVA), Switzerland, to Barcelona-El Prat Airport (BCN), Spain.
The aircraft (registration EC-HQJ) began its flight at 08:41 local time (UTC + 1) on November 17, 2017. As it taxed towards runway 05 GVA, the Airbus A320 was behind a Cessna Citation Excel, a jet company owned by NetJets. Air traffic control (ATC) instructed both aircraft to maintain their positions in the designation holding zone near runway 05.
At 8:51 a.m., the Cessna departed for its intended destination. A minute later, ATC cleared the Vueling A320 for take-off from GVA, which it did. At this time, the flight crew did not notice any irregularities in their oxygen supply or the air quality in the cabin. However, four minutes after takeoff and following the retraction of the landing gear, the two pilots discussed the “thick exhaust gases emitted by the Cessna Citation”.
According to the BEA report made public on November 3, 2020, the captain, who was the pilot flying, felt “almost nauseous”, while the first officer, the pilot who was watching, added that there had “a very strong odor”. The crew, still in contact with Geneva ATC, asked what type of Cessna Citation preceded them, to which ATC replied that there was no traffic ahead. The captain responded that there had been a Cessna Citation prior to departure and said he would file a report because of the odors in the cockpit. As ATC informed them of the type of aircraft ahead of them before takeoff, both pilots indicated that they were not feeling well. Subsequently, the captain proposed to increase the air intake to purify the air in the cabin.
Seven minutes after takeoff, the Vueling Airbus A320 was transferred to the control center en route to Marseille and proceeded to climb to flight level (FL) 290. Shortly after, the crew called the marshal. flight attendant and asked him if he had experienced any strange smells inside the main cabin, to which the flight attendant replied in the negative. The A320 captain asked the flight attendant to leave the cabin door open and the cabin crew to watch the two pilots in case something turned south.
The four-color pilot informed his colleague that he was feeling nauseous again, to which the first officer responded by deploying the oxygen masks in the cabin. The captain put on his mask, while the FO walked to the washroom. After his return, the captain asked his teammate how he was feeling. While the pilot replied that he had already felt nauseous, he “felt a little better” by the time, French investigators noted.
After a brief discussion in the cockpit about their choice of an alternative airport, the crew decided that in an emergency they would attempt an emergency landing at Marseille Provence Airport (MRS). While the BEA did not show any deterioration in the condition of either of the pilots, the co-pilot put on his oxygen mask and one minute after doing so, the crew put on his oxygen mask. declared PAN PAN and requested ATC to divert to Marseille, France.
At 9:30 am local time (UTC +1), the crew did not identify any anomalies concerning their state of health. Six minutes later, the crew landed at the French airport without incident. Emergency services encountered the Airbus A320 on the tarmac and the two pilots were taken to hospital for blood tests to check if the pilots suffered carbon monoxide poisoning. After testing and a brief period of surveillance, hospital workers released the hospital’s captain and first officer.
The blood tests did not indicate anything abnormal, while no other toxicological analysis was carried out, noted the BEA. However, nausea and dizziness persisted for a few days, including periods of respite, the French agency added.
Confusion leading to hypotheses
The BEA, anxious to identify the cause of the partial incapacity, has raised a few hypotheses. A food poisoning hypothesis was dismissed almost immediately, as the crew had not experienced any digestive issues and symptoms emerged following reports of strange smells inside the cockpit. Air contamination after defrost was also ruled out, as no defrost event occurred upon departure. Investigators were left with a riddle.
Maintenance personnel at the airport performed a task, designated by the aircraft manufacturer, to look for a potential source of cabin odor. Called the TSM task 05-50-00-810-831-A – Identifying the cause of odors or smoke in the cabin in the Airbus A320 manual, the task typically examines the Auxiliary Power Unit (APU ), both engines, bird strikes, problems with the aircraft’s air conditioning packs (PACK 1 & PACK 2) as a potential cause of odor or smoke in the cabin. The TSM task did not indicate anything abnormal, nor did the subsequent engine tests performed by the engineers on the ground. A few days after the incident, the Airbus A320 received a C-Check. The 20-month scheduled service check, with particular attention paid to the tightness of the seals that contain the lubricants of the rotating parts of the engines and the APU, revealed that everything was in order.
Attention was drawn to the Cessna Citation. The BEA said the business aircraft entered maintenance on August 16, 2020 and was returned to service on September 29, 2017, shortly before the incident. The aircraft’s right engine was removed and Pratt & Whitney, the jet engine’s PW545C engine builder, performed scheduled maintenance on the turbojet engine.
After interviews with the NetJets flight crew, a request to search for a potential oil leak, and nothing in the aircraft’s tech log, investigators found themselves again in a bind. Even a special event, namely that the metal chip detector on the left engine was activated on November 19, 2017, did not show anything. The event was recorded in the Cessna Citation Excel technical log and an oil sample was tested. Again, investigators found that all was well under the engine hood.
French accident investigators then looked into the possibility of contamination of the air outside.
Data from the Cockpit Voice Recorder (CVR) revealed that there was a connection between the two pilots who felt a strange odor in the cockpit and the Cessna Citation in front of them. The Airbus A320 remained behind the private jet for nearly four minutes.
The two aircraft engines are located at a height of approximately two meters above the ground. Thus, with the Vueling aircraft on hold for nearly four minutes in front of the Cessna, conditions allowed a concentration of exhaust gases to form in front of the narrow-body Airbus. Subsequently, the exhaust gases could have been drawn in by the CFM56-5B engines. Combined with the fact that the air in the cockpit and the cabin are different and that 60% of the air in the cockpit comes from the Air Conditioning Pressurization Kit (PACK) 1 located in the left engine when the cross purge valve is closed , and the faster airflow in the cockpit, it was possible that the exhaust gases were more concentrated in the cockpit than in the main cabin. Thus, this could have been the reason why the flight attendant could not identify any kind of odor in the part of the metal tube where the passengers usually sit.
In addition, the Cessna Citation’s metal chip detector alerted its flight crew to a potential problem with the left engine, the same engine where PACK 1 is located on the Airbus A320.
The negative results in the hospital could be explained by the time elapsed between the potential poisoning and the tests, in addition to the use of oxygen masks by the pilots. Nonetheless, the crew described the odor as pungent and sour, which is generally associated with nitrogen oxide (NOx) and sulfur dioxide (SO2). Both gases are emitted as a result of the combustion process on board an aircraft, according to the BEA report. Investigators also looked at possible contamination with tricresyl phosphate (TCP), which could sometimes also turn into tri-ortho-cresyl phosphate (ToCP). The chemicals are found in engine oil, which can sometimes seep into the compression system. Again, no contamination was found after samples from various aircraft filters were sent to an independent lab.
Even after sampling the crew’s hair for possible contamination, the results once again left investigators empty-handed.
“Despite the wide range of actions taken, the investigation failed to identify in a factual way what caused the symptoms and the physical discomfort of the flight crew,” the BEA concluded. The most likely hypothesis was that the crew inhaled an excessive amount of gas from the Cessna Citation’s exhaust system, read the investigation report.
“However, it is not excluded that the crew were intoxicated by another substance which either quickly disappeared or was not specifically looked for in the samples. [taken from the aircraft]BEA added.
Basis to investigate
The lesson to be learned here, the report concludes, is that investigators cannot act alone in cases where cabin air quality is in question. The use of pre-agreed agreements between airlines, airports and emergency services would allow emergency services to immediately conduct medical examinations, leading to a more definitive conclusion later.
A fatal example of an incapacitated crew could be Helios Airways flight 552, after which the crew of a Boeing 737 flying from Larnaca, Cyprus, to Prague, Czechia, via Athens, Greece, is become incapable. The crucial difference between the two incidents was that the Helios Airways crash was related to the loss of cabin pressure on board.
The loss of pressure in the cabin is due to the fact that the pilots of the airline did not recognize that the pressurization system was set in manual mode. They failed to identify the true nature of the problem and crashed just outside of Athens, Greece. Although the conditions were different, the end result could have been potentially fatal for those on board Vueling flight VY6204.