Published: 10 December 2021
(This article belongs to the Special Issue Aircraft Design (SI-3/2021))
‘Abstract
During its investigations into a series of ten aircraft crashes from 1979 to 1981, US National Transportation Safety Board (NTSB) officials were presented with a hypothesis that “several” of the crashes could have been caused by pilot impairment from breathing oil fumes inflight. The NTSB and their industry partners ultimately dismissed the hypothesis. The authors reviewed the crash reports, the mechanics of the relevant engine oil seals, and some engine bleed air data to consider whether the dismissal was justified. Four of the nine aircraft crash reports include details which are consistent with pilot impairment caused by breathing oil fumes. None of the tests of ground-based bleed air measurements of a subset of oil-based contaminants generated in the engine type on the crashed aircraft reproduced the inflight conditions that the accident investigators had flagged as potentially unsafe. The NTSB’s conclusion that the hypothesis of pilot incapacitation was “completely without validity” was inconsistent with the evidence. Parties with a commercial conflict of interest should not have played a role in the investigation of their products. There is enough evidence that pilots can be impaired by inhaling oil fumes to motivate more stringent design, operation, and reporting regulations to protect safety of flight.
Keywords: aircraft; accident; flight safety; fumes; engine oil; hydraulic fluid’
‘3.4. Regulations
Aircraft regulations stipulate that the cabin and flight deck ventilation supply systems must be designed to provide air that is “free from harmful or hazardous concentrations of gases and vapors” (14 CFR § 25.831(b)), which includes no more than 50 ppm of carbon monoxide and 5000 ppm of carbon dioxide (Table 4). Moreover, crews must be provided with “warning information” to alert them to unsafe conditions and enable them to take “appropriate corrective action” (14 CFR § 25.1309(c)) (Table 4). To date, though, these regulations have not been applied to monitor contaminants in the cabin air and alert pilots to the presence of oil fumes.
In addition to the design regulations, U.S. airlines are required to comply with three FAA reporting regulations for fume events (Table 4), but all are underutilized [22].’
‘6. Recommendations
For current aircraft that are equipped with bleed air systems, engineering control measures such as sensors and filters should be mandated to prevent inflight exposure to fumes and, thus, improve flight safety. For new aircraft types, non-bleed air supply systems should be standard.
Given the flight safety implications, all crewmembers should be trained to recognize and respond to the presence of bleed air contaminants [61].
The NTSB should reopen the 1984 report and update the conclusions based on what was known then about oil fumes and flight safety, and considering the data and reports published since then. The NTSB should also issue recommendations to the FAA on necessary actions to minimize the flight safety impacts of exposure to oil fumes.
Until suitably protective measures are implemented fleet-wide, the NTSB should consider pilot impairment from bleed-sourced fumes as a potential casual factor in future aircraft accident investigations. This is particularly important when an accident includes either relevant maintenance history or a pilot’s failure to communicate, for example.
If only to avoid the appearance of bias, future investigations should be independent of all commercial interests. Even though it is not unusual for the NTSB to include the FAA and manufacturers in accident investigations, both the poorly conceived design of the air sampling trials and the sweeping conclusions, suggest that commercial conflicts influenced this project.’
https://www.mdpi.com/2226-4310/8/12/389/htm