Turn-backs in or above an OTS require special consideration. Iyengar, who captains a Bombardier Challenger 605, and in another job also flew left seat in a Gulfstream 550 on many Atlantic transits, advises, “Always have a contingency plan and really know it in the event you're above the track system and have an emergency and have to descend. Know ahead of time which way you will have to turn if you need to go back.

“In business aviation,” he continued, “many times we will fly across the Atlantic on a random route above the tracks, often against the traffic. So you have to be very aware of where the tracks are and have a plan on which way you will turn if you have a problem. The worst case scenario is that you will be flying diagonally across the tracks above FL 410 and have a problem that needs you to do either an emergency descent or a drift-down, and so you really need to know where the tracks are because you are going to want to go down between them. So always know where you are relative to them.”

Stohr related a couple of tales of business aviation flight crews who were less than careful in managing their descents after experiencing emergencies. “A few years ago a business jet developed a pressurization problem requiring a descent. The crew proceeded direct Shannon and, in cutting across and descending through the tracks, caused a TCAS traffic advisory with two airliners and a resolution advisory for a third airliner.

“Another business jet developed a pressurization problem, as well,” he continued, “and the crew turned to a heading of 015 and descended, causing TCAS advisories for several airliners. Contingencies are written so that they will put aircraft in a position where they are least likely to conflict with other aircraft, based on the oceanic structure.” The moral is simple: Fly them as they're intended to be flown.

Iyengar “highly recommends” that when flight crews are receiving simulator training, to practice the contingency scenario and see how their aircraft perform and how they drift down. “Believe me, you will be surprised at how much lateral difference it takes to make a 180-deg. turn in case you have to go back to your origin or to reach your closest alternate. In the Gulfstream 550, depending on your weight, it will take 15 to 18 nm to make that turn.”

He even provided a simulator training scenario, in this case for the G550: FL 430, ISA conditions, Mach 0.83, 66,000 lb. “With one engine failed and the other at full power, drift-down took 55 sec. to slow to Mach 0.78 and 31,900 ft., and 4 min. and 20 mi. to make a 180-deg. turn in the descent. At FL 290, it took 3.4 min. and 18 mi. to make the 180-deg. turn. If you are sufficiently high above the tracks, you have to immediately make the turn before descending through the tracks or, if not, you must descend through and below the track structure before making the turn.”

So, based on your simulator experience, compile a plan of how you would pull off this maneuver if you ever had to do it. “You have to be on the ball and know what your plan will be,” Iyengar said. Especially if having to descend from a random route above the tracks, “you are penetrating into a structure where there are a lot of other aircraft.”

We ran this by trainer Stohr, who stressed, “If you need to go back, make sure you can make the turn within 15 nm; however, if you can't and overshoot the offset, continue the turn beyond 180 deg. to intercept it.” Thus the turn off track would be immediately initiated and maintained until an intercept heading back to the 15-nm offset has been established. “The procedure specifically states that, based on the performance of the aircraft the 15-nm offset is expected to be overshot,” Stohr explained. If operating within [the forthcoming] 25-nm lateral separation on the NATS, “extreme caution” must be exercised regarding now-opposite direction traffic on the adjacent track. Stohr also recommended that a climb or descent should be completed preferably before approaching within 10 nm of any adjacent track.

OK, so now you're backtracking. How are you going to navigate? “Invert the flight plan, if you have to reverse,” Stohr suggested. “Use the FMS, if the one in your airplane has the capability to invert, or preload a reverse flight plan before the flight.” Note: If you've been able to contact ATC to receive an amended clearance, then fly the new clearance.

Space prohibits a discussion of loss of communications and navigation and weather-deviation procedures, and readers are referred to ICAO and regional documents for full descriptions. The accompanying sidebar describes how to obtain these references plus relevant NATS documents supporting media.