Smoke Triggers More Diverted Flights Than Engine Problems

Air Safety Week, Oct 20, 2003

During the cruise phase of flight, a "smoke" event is more than twice as likely to cause an unscheduled landing than an engine problem, according to a new study of service difficulty reports.

Capt. Jim Shaw of the Air Line Pilots Association (ALPA) did the study. Shaw flies for Delta Air Lines (NYSE: DAL) and the findings clearly have implications for extended-range operations (EROPS). The extension of EROPS flight planning to 180 minutes from a divert airfield is predicated largely on engine reliability, and the steps taken in design, maintenance and flight planning for twinjets to preclude the loss of the second engine should the first have to be shut down (see ASW, March 24, March 31). Shaw's study suggests that crews on EROPS flights are more likely to face an in-flight smoke event, and that this potential threat to the safety of ever-longer EROPS flights may warrant elevated priority. His findings are consistent with reports submitted to the Aviation Safety Reporting System (ASRS), which show - among other things - that the proliferation of in-flight entertainment systems has increased the potential for smoke and fire events, for which aircrews may lack training, emergency equipment, and the ability to pinpoint and isolate the source of smoke (see ASW, Sept. 22).

In the process of examining hundreds of service difficulty reports (SDRs), Shaw originally concentrated on unscheduled landings due to engine problems. During the process of this examination, he found a surprisingly large number of smoke events that also were forcing crews to divert and land.

Shaw looked at unscheduled landings for a variety of two, three and fourengine aircraft, including the A330, B757, B767 and B777 twinjets, the MD-11 trijet, and the four-engine B747. The SDRs were filed over the 2000-2002 time frame, so Shaw basically was analyzing the most current data available.

His findings need to be couched with a disclaimer. Carrier participation in the SDR program varies widely. This being the case, rates cannot be derived from the SDR data. Moreover, the total number of SDR reports can be a misleading indicator of the number of events actually occurring. The actual number could be twice that reported to the SDR database.

Furthermore, while the aircraft selected for the review often are used in EROPS flights, the reported diverts did not all occur during the EROPS portion of the flight.

With these caveats in mind, Shaw's study is nonetheless significant. It points to the greater likelihood that crews on EROPS flights are more likely to face a smoke incident than an engine event serious enough to force landing at a divert airfield. "An EROPS flight must operate for an extended period of time with whatever condition caused the crew to begin the divert," Shaw said.

In comparing smoke to engine related unscheduled landings in the cruise portion of flight, Shaw found 59 reports of engine-related diverts, but more than 130 events where smoke triggered the decision to divert.

The findings suggest there is a real dilemma posed to crews by smoke," Shaw wrote. "Current regulations only require that once the smoke generation stops, the air ventilation system must be able to clear the cockpit of smoke within a preset time limit."

"Current regulations do not deal adequately with the problem of continuous smoke generation, which so often is a feature of the more serious smoke and fire events, such as the ValuJet Flight 592 crash and the Swissair Flight 111 accident," Shaw wrote.

With current aircraft designs based on the limited ability to clear the cockpit of smoke after the smoke stops being generated, Shaw asserted that "crews and passengers on EROPS aircraft are placed in the difficult position of trying to operate and survive for long periods of time in a smoke-filled aircraft."

To mitigate the risk, Shaw believes several options are available. "First, reduce the risk of fire or smoke through more rigorous wiring and flammability standards," he wrote.

"Next, get the fire or smoke generation stopped as soon as possible with improved fire detection and suppression in inaccessible areas," he wrote, citing specifically the need for detection and suppression in the attic space above the cabin and cockpit. (For vivid examples, see ASW, April 21)

"Finally," Shaw urged, "devices to improve instrument visibility in a smoke-filled cockpit, improved checklist procedures for dealing with smoke, and an adequate oxygen supply so the pilots at least have a chance of completing the divert when all else fails."

Some additional thoughts come to mind. To qualify for EROPS, an operator must demonstrate a specified in-flight shut down (IFSD) rate, thereby assuring regulators that its maintenance and other practices are sufficient to minimize the likelihood of engine problems in flight. Perhaps a comparable standard could be established for in-flight smoke events. Moreover, just as EROPS-certified airplanes must feature more backup systems, perhaps video smoke detection should be a required capability built into EROPS aircraft. One of the greatest challenges in dealing with an in-flight smoke event is reliably locating the source. In this regard, video smoke detection could be a critically-helpful tool.