Controversy Continues Over Long Distance Twin-Engine Flights

Air Safety Week, August 9, 1999

A request to extend the diversion time from 180 to 207 minutes for twin-jets in the event of an engine loss could lead to a thorough review of the regulations worldwide.

Indeed, a comprehensive assessment of the regulatory situation is years overdue, according to numerous sources.

The tale begins with a February 26, 1999 request from the Air Transport Association (ATA) and the Air Line Pilots Association (ALPA) to extend the upper limit of ETOPS (extended twin-engine operations) from 180 minutes to 207 minutes. The request would allow Boeing's [BA] formidable B777 greater flexibility in flying Northern Pacific routes. The Federal Aviation Administration (FAA) asked the industry for comment. That invitation has generated nearly three dozen responses (see ASW, June 21). The most recent was a 20-page July 7 submission from Boeing, commenting on the comments submitted before the docket was closed.

In its latest comment, Boeing argues that winter operations in the North Pacific do not necessarily involve a harsher environment than in the North Atlantic. The North Pacific is the primary area of interest for 207 minute ETOPS. "Most of the alternates used for North Pacific operations (with the exception of Anadyr) are actually south of Anchorage, while Anadyr lies at approximately the same latitude as Iqaluit, an airport commonly relied upon in North Atlantic operations," Boeing asserted.

However, the Gulf Stream in the Atlantic does have a warming effect at higher latitudes that is not present in the Pacific. In its May 26 comment, the European Association of Aerospace Industries (AECMA) argued that the Pacific truly represents a more extreme situation. AECMA argued that in the case of a diversionary winter landing at some of the primitive airfields under consideration, "most of the evacuees would not survive after only a few minutes on the ground."

Although not an ETOPS flight, AECMA cited a forced landing by a Russian aircraft in the region where, despite the rapid action of rescue/firefighting crews, all the occupants died from the cold temperature.

In addition to the environmental factors, AECMA was one of the few organizations to raise the specter of multiple systems failure: "A number of ETOPS flights (of both Airbus and Boeing aircraft) were affected by combinations of failures that might have prevented the crew to cope with aggravating adverse operating conditions...such as multiple electrical failures, multiple hydraulic failures and successive failures or malfunctions of both engines. Some of these events were caused by maintenance errors resulting in time-dependent situations...(e.g., slow oil leak or slow hydraulic fluid leak)."

Had they occurred in the wider expanses of the North Pacific, AECMA intoned, "...at least three of these events would have had a high probability of ending in catastrophe."

Boeing clearly does not hew to any suggestion that the safety margins are being reduced by extending ETOPS from 180 to 207 minutes. In fact, Boeing argues that specified suitability is not a limitation, per se: "Thus, the Type Certificate Data Sheet states that the 777 is suited to 180-minute ETOPS, but it does not indicate a limitation to 180-minute ETOPS (emphasis in original)."

The widely divergent views in the comments place the ETOPS ball, as it were, in the FAA's court. As a next step, the agency must issue a proposed action, and that is expected by the end of this year.

In the meantime, based on interviews and a review of all comments in the docket, we present here three ETOPS scenarios. They illustrate the range of potential problems under consideration:

* Scenario #1: A "benign" engine failure. Fair weather. Summer. While the in-flight shutdown rate of modern jet engines reflects their high level of reliability, 1 shutdown for every 250,000 hours for the Rolls Royce Trent engine, for example, they do occur. Assume in this case an in-flight shutdown high over the Pacific at 39,000 feet, 180 minutes' flying from a divert airfield, with no other mechanical or system problems. Assume also that the engine's fan section can still rotate ("free wheel") in the airstream; in other words it has not "seized," turning into the equivalent of a flat plate and adding terrifically to drag.

What happens? Unable to maintain current altitude and speed, the crew sets the remaining engine at maximum continuous thrust (engines have been tested at this thrust level for 3 hours) and the aircraft "drifts down" over a 15-30 minute period to a stabilized altitude that can be maintained. Depending upon aircraft gross weight, the stabilized altitude will be somewhere in the range of 20,000-25,000 feet. In other words, the loss of one engine means the inevitable loss of about 15,000 feet in altitude. Cabin pressure and temperature is maintained by the bleed air from the one remaining engine. The aircraft retains ample electrical generation capability from the remaining engine's generator. The auxiliary power unit (APU) might be started to provide an additional margin of electrical generating capacity. The crew may shut down galley, in-flight entertainment and other non-essential systems to reduce the electrical load.