United B763 over Atlantic on Jan 19th 2018, 15 people felt unwell
Last Update: October 5, 2020 / 10:51:36 GMT/Zulu time
Incident Facts
Date of incident
Jan 19, 2018
Classification
Incident
Airline
United
Flight number
UA-71
Departure
Amsterdam, Netherlands
Destination
Newark, United States
Aircraft Registration
N644UA
Aircraft Type
Boeing 767-300
ICAO Type Designator
B763
Passengers reported a bad odour making them feeling sick, other passengers reported lack of oxygen.
The airline however suspected an acute outbreak of flu or food poisoning reporting a check of the aircraft had not found anything out of the ordinary.
The Dutch Safety Board advised they have opened an investigation after a number of occupants of the aircraft felt unwell.
On Oct 5th 2020 the DSB reported in their quarterly bulletin, that the occurrence was not extensively investigated although rated a serious incident. The DSB summarized the sequence of events:
An hour into the flight, while flying straight and level at FL320 over Scotland, a growing number of the aeroplane’s occupants indicated they were not feeling well. Eventually all cabin crew and fifteen passengers (most of them from rows 27 through 30) were reporting similar symptoms. These included blurred vision, sensations of the aeroplane banking to the right and climbing, nausea and a general feeling of drowsiness.
While cabin pressure altitude was confirmed to be normal at around 8,000 feet, pulse oximeter readings with the cabin crew indicated low blood oxygen saturation levels. Administering oxygen and medication against motion sickness did not lead to structural improvements. Two hours into the flight, the captain instructed the cabin crew to stop their duties and decided to return to Schiphol for a precautionary landing.
The aeroplane made an overweight landing as a result of the smaller-than-planned amount of fuel used, and was directed to a remote parking position. There, one of the main wheel brakes overheated and the tyre thermal fuse plug blew, allowing the tyre to deflate to prevent a tire burst. The aeroplane did not sustain any further damage. No one got injured.
After the brakes had cooled, fourteen sick passengers were taken off the aeroplane for tests by airport medical services. These tests (anamnesis, blood pressure, oxygen saturation, ECG) did not yield any abnormal results. All passengers indicated that their symptoms disappeared as the doors were opened and fresh air entered the cabin. The cabin crew members were taken to a mobile medical facility set up near the aeroplane. Three of them were still showing some symptoms, most notably high blood pressure. One person showed high blood carbon monoxide levels, but the measuring equipment used was later suspected to be unreliable. All three were given extra oxygen after which all symptoms disappeared. No blood or urine samples were collected. The flight crew never suffered any symptoms. There was no need for any of the occupants to go to hospital.
The DSB described the steps taken by the investigation:
The investigation focused on probable causes of the cabin crew members’ and passengers’ symptoms, rather than on flight crew crisis management, the overweight landing, or the emergency services at the airport. Flight data recorder (FDR) data from the event flight, as well as the three previous (nominal) flights, were downloaded and analysed. The analysis did not indicate an increased likelihood of motion sickness on this flight, relative to the preceding nominal flights. Furthermore, Significant Weather Charts of 0600 and 1200 UTC on 19 January 2018 mentioned no significant weather on the route between Amsterdam and Ireland.
The aeroplane’s environmental control system (ECS) uses bleed air from the compressor of its Pratt & Whitney PW4000 turbofan engines for pressurized cabin air supply and controls cabin temperature and humidity. 50% of this conditioned cabin air is filtered and recirculated. Inspection of the aeroplane on the day after the event revealed a small puddle of synthetic motor oil at the 6 o’clock position in the fan cowling of the right-hand engine (#2). According to the aeroplane’s maintenance manual this is not unusual and may occur during wind milling or engine shutdown. Engine maintenance records demonstrated that both engines’ oil consumption had been within limits during the previous ten flights.
At the right-hand inner tube that connects the ECS bleed air inlet to the ozone converter outlet, a powdery black substance was found. This material contained small amounts of pentaerythritol triesters and tricresyl phosphate (TCP) isomers also found in the oil in the #2 engine cowling, very small amounts of some triglycerides used in lubricants, and paraffin. At the intake of the right-hand air recycling fan, an oily substance was found containing dioctyl sebacate (DOS), which is used in plastics, lubricants and flame retardant.
While the crew had not noticed any abnormal smells during the flight, it was decided to measure cabin air levels of oxygen, and of carbon monoxide and other intoxicating gasses or fumes which may originate from oil or de-icing fluid leaking into the ECS. Concentrations of toxic substances like volatile organic compounds (including organophosphate esters/TCP and aldehydes) were also measured. Nothing out of the ordinary was found during either high and low power engine test runs at Schiphol, or a flight test performed by the operator in the United States a week after the event. However, as all measurements were carried out after the cabin had been ventilated, cabin air contamination during the event flight could not be ruled out.
Based on the data available and previous occurrences on this type of aeroplane, the manufacturer concluded that the events were likely caused by degraded and uneven airflow and/or temperature control issues in the cabin. Local blockage of airflow in the conditioned air distribution system may be caused by ambient air contamination, internal lining from ground conditioned air hoses, wrappers of papers or debris from degraded recirculation air filters. The manufacturer therefore issued a service letter to operators, suggesting the implementation of a maintenance program to clean the air distribution system on a regular basis.
The Dutch Safety Board was able to exclude a number of other factors (including intoxication from food or beverages, infectious diseases, and leakage from oxygen bottles, pantry ovens or fire extinguishers in the cabin) that might contribute to the experienced symptoms. However, conclusive evidence regarding their probable cause was not found.
Aircraft Registration Data
Incident Facts
Date of incident
Jan 19, 2018
Classification
Incident
Airline
United
Flight number
UA-71
Departure
Amsterdam, Netherlands
Destination
Newark, United States
Aircraft Registration
N644UA
Aircraft Type
Boeing 767-300
ICAO Type Designator
B763
This article is published under license from Avherald.com. © of text by Avherald.com.
Article source
You can read 2 more free articles without a subscription.
Subscribe now and continue reading without any limits!
Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.
Send tip
Support AeroInside by sending a small tip amount.
Related articles
United B763 near Providence on Apr 22nd 2024, suspected fuel leak
A United Boeing 767-300, registration N644UA performing flight UA-108 from Washington Dulles,DC (USA) to Munich (Germany), was enroute at FL330 about…
United B789 near San Francisco on Apr 19th 2024, cargo smoke indication
A United Boeing 787-9, registration N15969 performing flight UA-801 from Los Angeles,CA (USA) to Hong Kong (China), was enroute at FL340 about 30nm…
United B753 enroute on Apr 10th 2024, Rockies' coach in captain's seat
A United Boeing 757-300, registration N73860 performing charter flight UA-3779 from Denver,CO (USA) to Toronto,ON (Canada) with the Colorado Rockies…
United B738 at Las Vegas on Apr 10th 2024, dropped panel in flight
A United Boeing 737-800, registration N24224 performing flight UA-1960 from Los Angeles,CA to Las Vegas,NV (USA), concluded a seemingly uneventful…
United B772 at Rome on Apr 5th 2024, engine compressor stall
A United Boeing 777-200, registration N209UA performing flight UA-885 from Rome Fiumicino (Italy) to Washington Dulles,DC (USA), was climbing through…
Newest articles
LATAM A321 at Sao Paulo on Apr 26th 2024, tail scrape on takeoff
A LATAM Brasil Airbus A321-200, registration PT-MXO performing flight LA-4518 from Sao Paulo Guarulhos,SP to Florianopolis,(Brazil), was departing…
Airblue A21N at Lahore on Jul 26th 2022, cargo smoke warning
An Airblue Airbus A321-200N, registration AP-BOE performing flight PA-412 from Lahore (Pakistan) to Sharjah (United Arab Emirates), was climbing out…
Subscribe today
Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.
Pick your plan and subscribePartner
A new way to document and demonstrate airworthiness compliance and aircraft value. Find out more.
ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.
Your regulation partner, specialists in aviation safety and compliance; providing training, auditing, and consultancy services. Find out more.
AeroInside Blog
Popular aircraft
Airbus A320Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American AirlinesUnited
Delta
Air Canada
Lufthansa
British Airways