One Engine Inoperative Takeoff Planning

July 16, 2012

It can be terribly frustrating. You’re planning your departure, but find that your aircraft is unable to fly the standard instrument departure (SID) with one engine inoperative (OEI). You consider your choices: You could ask for another SID, offload or take on less fuel to lighten your takeoff weight. You might even be forced to delay your flight or make other changes that affect your operations and your passengers.

But what if you didn’t have to do any of that?

“Many operators aren’t aware that there are alternative procedures for OEI takeoff planning,” said NBAA Domestic Operations Committee member Steve Leon. As a member of NBAA’s Domestic Operations Committee, he is the principle author of a white paper titled, “One Engine Inoperative Takeoff Planning and Climb Performance.” Its objective: “To promote operator knowledge, operator application, and operator training issues surrounding transport airplane takeoff performance, Part 91 and 135 operators alike, specifically showing that the current practice of planning for OEI takeoff obstacle avoidance and compliance with TERPS criteria is inadequate and potentially dangerous.”

At the root of this discussion is the fact that terminal instrument procedures (TERPS) climb requirements are predicated on nominal performance values – all engines running. Often, the procedures are in place to accommodate air traffic control functions and noise abatement and not solely obstacle clearance. In addition, many do not take into account obstacles that are low and close-in.

“TERPS were developed for normal operations,” Leon explained. “They require certain climb gradients within the realm of normal operations. An engine out situation is considered to be an emergency, and an operator can deviate to meet the emergency.”

That ability to deviate is outlined in FAA Advisory Circular 120-91, “Airport Obstacle Analysis,” which provides guidance to large transport category aircraft operators in the development of OEI procedures found in Part 135, Subpart I.

That subpart states operators must have a procedure to avoid obstacles in the event of an OEI takeoff. As long as your aircraft can meet or exceed the climb gradients published in the SID/ODP pertaining to the runway you are using for departure, you do not have to decline the SID or ODP. You don’t have to delay your takeoff in hopes of better weather, and you don’t have to reduce your payload.

“You can’t just wing it,” Leon said. “You still must have a plan for OEI takeoff. That’s mandatory. But you don’t have to follow the SID.”

What are the alternatives?

“You can purchase an OEI takeoff procedure from a commercial vendor or you can develop one yourself. But there are drawbacks. Purchasing a plan can be expensive. Developing one yourself is extremely difficult and time consuming,” Leon added. That is why so many flightcrews wind up depending on the SIDs.

“But depending on the SID means you’re relying on a procedure that was never meant for OEI takeoffs and that has its challenges too, both from a safety and an operational standpoint,” he noted.