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

Let’s pick this up right where the glide range calculation left off. We’ve already worked out that in still air, after an engine failure, this single-engine Class B aeroplane covers a horizontal glide distance of 142,857 feet, which is roughly 23.5 nautical miles. That number is the key to the whole en-route planning rule. Here’s the logic. If the aeroplane can only glide 23.5 NM in still air, then it must never be further than 23.5 NM from a safe forced landing location. So the way we plan the route is this: around each safe forced landing location — those are the yellow dots on the chart — we draw a circle with a radius of 23.5 NM. That circle is the glide descent range around that field. Then we draw our track line from Airfield A to Airfield B so that it stays inside every circle it passes near. If the flight track falls outside any of 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 — the track must remain within glide range of each field at all times. Now, here’s the important operational lever: altitude. If the aeroplane operates at a higher altitude, it covers a greater distance in the glide after engine failure. The example in front of us makes this concrete. Operating at 15,000 feet instead of 10,000 feet increases the still air glide range from 23.5 NM up to 35 nautical miles. So the circles around each forced landing location grow — they get bigger in radius because the glide range has grown. And that changes the route planning completely. With the bigger circles, the aeroplane can now fly along a straight track from Airfield A to Airfield B, because at all times throughout the flight it is within glide range of a suitable forced landing location. That’s the practical consequence: small piston engine aeroplanes should be flown at their maximum altitudes so that direct routes can be achieved. But — and this is where the regulation bites — you cannot simply climb as high as you like and claim the benefit. There is a rule that limits the altitude you may use in the calculation. That rule is 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. “Maximum continuous power” is the highest power setting the engine can sustain continuously without damage — it’s not take-off power, it’s the sustained cruise setting. The rule says you may not assume the engine is producing that maximum continuous power at an altitude higher than the one where the aeroplane’s rate of climb has fallen to 300 feet per minute. In other words, there is a specific altitude — the altitude at which the rate of climb is exactly 300 ft/min — and that altitude is the ceiling you are allowed to use in your glide range calculation. What this rule effectively does is limit the maximum altitude that can be used in order to comply with the forced landing rule. So here’s the subtlety, and I want you to get this exactly right: the aeroplane may physically operate at a higher altitude than this regulation prescribes — nothing stops you climbing higher — but the operator may not use that higher altitude in the calculation of glide range to a safe landing area. So if you fly at 20,000 feet but the regulation ceiling is 12,000 feet, you must still plan your forced landing circles using the glide range from 12,000 feet. The higher altitude gives you no credit in the calculation. So the complete picture for en-route and descent planning on a single-engine Class B aeroplane is this: compute the still air glide range from the regulation-limited altitude, draw circles of that radius around every safe forced landing location, and keep your track inside those circles. Higher altitude gives you bigger circles and straighter tracks, but only up to the altitude where rate of climb equals 300 ft/min at maximum continuous power. Beyond that, the extra height is operationally real but legally invisible to your forced landing planning.