4 Abandoning the tow
4.1 Abort Launch. 4.2 Communication Review. We at first habitually made a radio call from the pilot that "slack is out," but this is a hurried call at a moment when the pilot's spare hand is more properly on the release handle, in case of emergency, than keying a mike. I think that it should not be made, and because it's hurried is nearly always unintelligible anyway. In my judgment, the only radio call from the glider between "ready" and the time it's visibly airborne should be "abort," so that if an unintelligible call is received it is assumed to be an "abort" message. It is hazardous for the driver of the tow vehicle to abandon the tow: the glider pilot may have any situation well in hand, and once under way, speed provides control and altitude provides options. After analyzing all the situations I can think of, I have concluded that the only situations in which it is safer for the driver to abandon the tow than to continue it are those in which the glider is obviously out of a safe attitude. In such circumstances, damage and injury are almost certain to occur, and the goal of abandoning tow is to stop adding energy to a catastrophic failure. The most obvious example is when for any reason the glider is seen to be turning or steeply banked early in tow. Control-surface failure or a collision with a ground object are the most likely causes, and the incident might not be visible to the driver. Tow-rope anomalies are also considerations. The Blanik's ground launch bridle attaches to both sides of the fuselage. If one of these comes free and the other is not promptly released, the glider may yaw severely before control effectiveness is gained. I know of one accident in which this happened, but do not know the mechanism by which this occurred. The bridle attachment is via a very simple mechanism that is almost foolproof. However, it is possible to attach one clip insecurely. The crew member attaching the bridle must visually check to ensure that the clips are clean, that no debris is caught in the channel that holds the clips, that the central pin is fully extended, and that the pin moves both in and out freely when the release handle is operated. After they are engaged, it should be possible to jiggle them just a little. A tow rope otherwise pull asymmetrically if it were carelessly wrapped around a wing root or a loop wrapped around the empennage or tailwheel. This would be possible through carelessness, or if the tow vehicle slowed severely after the glider began to move, and the glider over-ran the rope, which then looped around some part of the glider's structure, and the tow vehicle accelerated again. I did have one incident in which the two vehicle lost power an the rope wrapped around the glider's wheel. I was very grateful that the driver abandoned the tow. He did so because after the momentary stall, he judged that remaining runway wouldn't permit a good launch; he had no idea of my predicament, nor did I, as I couldn't see the bottom of the glider from within the cockpit. The rope had been picked up by the wheel and wrapped around the main- wheel axle. It could as easily loop or wrap around the tailwheel, which would cause a catastrophic accident if the tow were continued. The antidote is simple: the tow must be abandoned if the tow vehicle slows for any reason, before the glider is airborne, after beginning tow. If the tow vehicle must abandon the tow for any reason, including a rope break, prior to completing a run to the far end of the runway, the most important action is to get out of the way. The glider must be permitted the broadest range of actions possible, and the driver should use judgment in deciding how best to do this. After this is done, and the glider is down safely, then the driver must make sure the vehicle is out of the way of other aircraft as well. The pilot must be prepared mentally, not only for a rope break that might occur at any time, but for a stall or malfunction of the tow vehicle, particularly during the critical low-altitude phases of the launch. 4.1 Abort Launch There is no satisfactory way to communicate an abort, in that we yearn for the message to be delivered instantaneously and telepathically, and we have to depend on error-prone mechanisms. An excited voice over the radio is often unintelligible; at the beginning of the launch the attention of both the driver and the pilot are focused intensely on the launch process; my experience is that most of the time neither of them will hear or understand any radio call until the glider is climbing securely. But the radio is the only way for driver and pilot to communicate directly. Ideally, the wing runner will have a hand- held, and should announce aborted takeoffs when they occur. Ultimately, the most effective way to communicate is with action: release the rope. The person at the other end will deal with the consequences. The tow vehicle should not normally release the rope prematurely, but should do so if it appears that the glider is out of control in any way. I think that it is better, if the glider is not definitely in trouble, to continue the tow, remaining alert to the need to release, especially early in climb, as while the glider is establishing the first part of the steep climb, premature rope release can precipitate a low-altitude stall. I believe that if the glider is seen to yaw severely, either on the ground or in the air, that release by the tow driver is probably the safest action. If the glider is still on the ground and is seen to deviate significantly from a straight course, except for the normal moderate yaw toward the down wing in a tow without a wing runner, the driver should immediately release. This will immediately stop energy transfer to the glider by releasing the elasticity in the rope. We have not experienced any mishaps in which the glider has yawed on takeoff, however. The tow vehicle should not abort at any time simply by stopping in the middle of the runway, as the glider may need the runway for landing: the truck should release the rope and quickly pull off to the side, outside the runway lights if any. The main idea is not to obstruct any landing options for the glider pilot. The driver therefore should head for the closest spot that is a really bad place for the glider to land. At the thrilling end of the rope, the pilot, who is Officially In Command of the operation, should lower the nose and release (two hands, two simultaneous actions) as soon as it's apparent something unusual is happening, without waiting to figure out exactly what that "something unusual" is. 4.2 Communication Review Let's offer a communication sequence. Here are the important items that should be covered: - Preflight inspection complete? - Have the driver and pilot agreed on tow speeds? - Rope release tested at both ends? - Glider positioned appropriately? - (In a tandem glider) Who is PIC? - Cockpit checklist complete? - Rope attached? - Tow vehicle in position, hooked up, and ready? - Pattern clear? - Ready to tow? - Signal start. Copyright © 2000, 2002 Daniel L. Johnson; all rights reserved.