This is the second in a two-part article. The first explored fires and issues when you need to land.
“Our Equal Time Point (ETP) was ahead of us but the situation wasn’t anything we had trained for…”
Twenty years ago (2003), our attitudes about drift down were more, shall we say, self-centered. “We are the emergency, everyone else can get out of our way.” We taught that if an engine fails, you set a specified maximum thrust on the operating engine, allow the speed to decay to a speed calculated to maximize your forward distance, and then you descended at that speed. If you were past the ETP--the position along your route that results in an equal time continuing forward as the time turning around--then you pressed on. Otherwise, you turned around.
I think most of us today know the decisions are rarely this cut and dried, but back then, I believed the popular theory. Until I was faced with reality.
We were flying a Challenger 604 from Europe to the United States at flight level 360 on the North Atlantic Track System (NATS), with airplanes above, below and to either side of us. Our Standard Operating Procedure required us to compute three ETPs. The one engine inoperative ETP considered the need to descend to an optimal altitude with one less engine and less speed. The loss of pressurization ETP assumed the need descend. Finally, the remain at altitude ETP was used for medical and other emergencies to minimize the remaining time in flight. While an ETP is computed using time, the “T” in the acronym, it is more properly thought of as geographic point, the “P” in ETP. Our company procedures required that we compute all three, but if all three were grouped within 100 nm of each other, only the middle point was plotted.
That was the case on this flight, and our ETP was at 53° 05.0’ North, 37° 17.3’ West. Passing the infamous 30 West waypoint, we made the necessary switch to Gander Oceanic on our high-frequency radio and busied ourselves with the many checklists triggered by waypoint passages. I briefed the other pilot that our ETP was still in front of us and that if we had any problems, the plan was to turn 180° back to Shannon. We would drift down in the turn if we lost an engine, complete a rapid descent if we lost pressurization, or remain at altitude if we could. “Obviously,” my fellow pilot said. “Obviously,” I agreed.
Back then we were required to take wind and temperature readings at each halfway point between waypoints and I was doing just that when an engine indication turned amber, letting us know one of our engines was vibrating excessively. The FAN VIB readout showed the left engine at 3.5 Mils, well above the 2.7 Mil limit. I pulled out the Quick Reference Handbook (QRH) and read. The fan is the first set of blades in the engine compressor section, and the largest. An excessive vibration risks separation of a blade with risk to the fuselage and the rest of the engine. The procedure called for us to reduce the throttle until the vibration was in limits. I did that, resulting in enough thrust loss that our Mach number decreased from our filed 0.80 Mach to 0.76 Mach. The procedure also called for the engine to be shut down if there were any other abnormal engine indications. There were not.
“Back to Shannon?” my fellow pilot asked. I stared at our plotting chart, which clearly indicated the ETP was still almost a hundred nm in front of us. “Give me a moment,” I said. “I need to think about this.”
I considered that turning around at this altitude would take us about 25 nm left or right, almost halving the distance between us and any aircraft on the next track and increasing the risk of running into an airliner carrying hundreds of passengers for the sake of the three we had onboard. But I also thought about losing the engine and wanting to minimize my distance to a runway should that happen. But how much distance would be taken by the turn itself?
Looking at the plotting chart, I thought that we might end up taking longer to turn around than pressing forward. Finally, I looked at the engines, both of which seemed to be operating fine, albeit one at a reduced thrust setting. “Let’s press on and let Gander know we have to slow down,” I finally said. “I’ll phone a friend,” using a phrase from a game show popular at the time.
I picked up our satellite phone and called our mechanic, who asked for a few minutes to speak with the good folks at General Electric, the engine manufacturer. A few minutes later our mechanic called back. “They’ve been seeing more and more of this lately,” he said. “They say there is a coating on the fan blades that sometimes delaminates and causes these indications. There isn’t any increased risk of the engine failing. Just keep the engine at or below where you have it and bring the airplane home.”
Sometimes the best decision is to delay and consider your options.
In some cases, a diversion decision needs to be made quickly because fuel and altitude are robbing you of time. In other cases, the best decision might be procrastination. A mid-oceanic diversion carries with it added risks that must be considered. Will drifting down put you into the path of another airplane? Do your ETP fuel computations consider the winds at lower altitude or any abnormal fuel burns that have taken you off your planned numbers? If the decision doesn’t have to be made immediately, perhaps it shouldn’t. Many in the Air Force used to say, “Flexibility is the key to air power.” To that I would add, “Procrastination is the key to flexibility.”
The Divert Decision
There are two, almost primal, motivations tugging at us when faced with a divert decision. As mission-oriented pilots, we want to press on to the destination. This isn’t “get home-itis,” it is mission accomplishment. But we are also highly trained to think in terms of action-reaction scenarios. “In case of ____, I will do ____.” Both instincts serve us well, until they don’t.
In the case of a cabin fire, a structural failure or any scenario where the ability to fly the airplane is in doubt, an immediate action may be necessary and the divert decision becomes easy. But for most situations, the right answer could be to take a breath and consider your options. It’s just like we used to say back in the days when bad things happened in the air almost routinely:
Question: “What’s the first thing you should do in the case of an inflight emergency, and when should you do it?
Answer: “You should do nothing, and you should do that immediately.”
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