Single-engine Class B - En Route and Descent — Page 317, Lesson 393

Right, so we've just worked out the glide range in still air. We found that after an engine failure, the aeroplane covers a horizontal distance of 142,857 feet, which is roughly 23.5 nautical miles. That's the key number we're carrying forward. Now, here's the operational consequence. Because the aeroplane can only glide 23.5 NM, it must never be further away than 23.5 NM from a safe forced landing location. So the planning method is this: you draw a circle of 23.5 NM radius around each safe forced landing location — those are the yellow dots on the chart. Then you draw your track line from Airfield A to Airfield B so that it stays within each circle. If your flight track falls outside those circles, then following an engine failure the aeroplane simply will not make it to a safe forced landing area. That's the whole constraint in a nutshell — the track must remain within glide range of each field at all times. Now, what happens if we change the altitude? If the aeroplane operates at a higher altitude, it covers a greater distance in the glide after engine failure. For example, operating at 15,000 feet instead of 10,000 feet increases the still air glide range to 35 nautical miles. So the circles around each forced landing location grow — they get bigger, as you can see in Figure 9.3. And that's the payoff. Notice that now the aeroplane can fly along a straight track to Airfield B, because at all times throughout the flight it is within glide range of a suitable forced landing location. So the practical conclusion is that small piston engine aeroplanes should be flown at their maximum altitudes so that direct routes can be achieved. But — and this is the important regulatory catch — when you're planning that altitude, another rule comes into play. That's EU-OPS 1.542 (b) (1). Let me read it carefully, because the wording matters. It states that when complying with the safe forced landing rule, the aeroplane must not be assumed to be flying with the engine operating at maximum continuous power at an altitude exceeding that at which the aeroplane's rate of climb equals 300 feet per minute. Let me unpack that. The rule effectively limits the maximum altitude you can use in your forced landing calculation. You find the altitude at which the aeroplane's rate of climb is exactly 300 feet per minute — that's your ceiling for planning purposes. You cannot assume the engine is at maximum continuous power above that altitude when you're calculating glide range to a safe landing area. Now, the subtlety: the aeroplane may operate at a higher altitude than this regulation prescribes. That's allowed. But the operator may not use that higher altitude in the calculation of glide range to a safe landing area. So you can fly higher, but you can't claim the extra glide distance in your planning. The circles stay based on the 300 ft/min rate-of-climb altitude, not your actual cruising altitude. So the full picture is: glide range sets the radius of your forced landing circles, higher altitude gives you bigger circles and straighter tracks, but EU-OPS 1.542 caps the altitude you're allowed to use for that calculation at the point where rate of climb equals 300 feet per minute.