Responding to a mandate from Congress to study the FAA’s oversight of cockpit smoke mitigation, the Government Accountability Office (GAO) has found that dense, continuous smoke occurs so infrequently that it was not practical for the GAO to reach a conclusion about the effectiveness of the FAA’s actions.

According to the watchdog agency, the NTSB and the FAA identified no accidents or incidents between 2002 and 2012 involving dense, continuous smoke in the cockpit.

In a footnote, however, the GAO revealed that neither the NTSB nor the FAA tracks the occurrence of dense, continuous smoke (perhaps explaining why the FAA was unable to identify any dense, continuous smoke events in the past 10 years) and a definitive determination could not be made for some events.

To identify stakeholders’ views on the effectiveness of the FAA’s oversight, the GAO said it reviewed relevant NTSB recommendations and interviewed 15 stakeholders representing various sectors of the aviation community, including officials from the FAA and NTSB; representatives from the Air Line Pilots Association and the Coalition of Airline Pilots Associations; Airlines for America; Boeing and Airbus; UPS and JetBlue Airways; the Flight Safety Foundation; a company that manufactures a device designed to mitigate the effects of dense, continuous smoke in the cockpit; and four aviation safety professionals.

The GAO conducted its performance audit from September last year through May, and it found that the FAA uses a variety of approaches–including certifying airplane design and inspecting airlines–to oversee procedures and technologies that prevent or mitigate the effects of dense, continuous smoke in the cockpit.

In the course of its review, the GAO identified five such procedures and technologies that the FAA oversees: evacuation of dense smoke from the cockpit; protective breathing equipment for the flight crew; pilot training on emergency procedures; a checklist to respond to smoke in the cockpit; and an emergency vision assurance system (EVAS).

EVAS consists of an inflatable transparent unit that provides the pilot with a “window” to view the instruments and out the windshield when there is dense, continuous smoke in the cockpit. Although the FAA has approved installation of the device for several models of commercial airplane, the agency concluded that EVAS does not provide a significant safety benefit and the potential benefits do not warrant the costs the industry would incur if the FAA were to mandate installation.

This is because dense, continuous smoke in the cockpit is a rare event, and, according to the FAA, accidents in which dense, continuous smoke has occurred indicate that such scenarios “are likely to be catastrophic for reasons other than flight crew visibility (for example, loss of airplane controllability, structural failure).” Further, the NTSB has identified dense, continuous smoke in the cockpit as the probable cause of only one commercial aviation accident–and it was not Swissair Flight 111, the MD-11 that crashed into the Atlantic Ocean off Nova Scotia in September 1998 after a fire broke out in the cockpit ceiling. The sole accident cited involved a Pan Am 707 that crashed in Boston nearly 40 years ago.