First, let's set the foundation — Page 349, Lesson 431

I want to walk you through the compliance rules for the en route phase with one engine inoperative. We've already covered the basic idea — that after an engine failure, you need to be able to get to an airfield to land. But the regulation doesn't just say "stay near an airfield." It has specific rules about how you prove compliance, and those rules are very similar to what we saw in the single-engine en route lesson. First, let's set the foundation. For the pilot to abide by the regulation, two things must be known: the descent range with one engine inoperative, and the one engine inoperative cruise range. Once you've calculated both, you plot a flight track that ensures an airfield is always within the total one engine inoperative descent distance. That's the core requirement — at every point along your route, an airfield must be reachable within that total descent distance. Now, here's where the compliance rules come in. They govern how that descent range is calculated. There are two rules, and I want you to hold onto both because they're precise. The first rule: The aeroplane must not be assumed to be flying at an altitude exceeding that at which the rate of climb equals 300 feet per minute with all engines operating, within the maximum continuous power conditions specified. Let me unpack that. You cannot assume you're cruising at some high altitude just to gain extra range. The regulation caps your assumed altitude at the point where your rate of climb — with all engines still working — is exactly 300 feet per minute, under maximum continuous power. So if your aircraft could climb higher, you don't get to use that extra altitude to stretch your descent range. The rule forces you to plan conservatively, at that 300 feet per minute altitude. The second rule: The assumed en route gradient with one engine inoperative shall be the gross gradient of descent or climb, as appropriate, respectively increased by a gradient of 0.5%, or decreased by a gradient of 0.5%. Let me break that down carefully. You take the gross gradient — that's the raw, unadjusted performance figure from the manufacturer. If you're in a descent, you increase that gradient by 0.5%. If you're in a climb, you decrease it by 0.5%. So for a descent, you make it steeper — worse for range — by adding half a percent. For a climb, you make it shallower — also worse — by subtracting half a percent. Either way, you're penalizing your performance to build in a safety margin. Now, what does the first rule actually mean in practice? It means the aeroplane must not use the extra altitude above that 300 feet per minute altitude to gain extra range to help comply with landing at an airfield after engine failure. So even if your aircraft is perfectly capable of cruising at a higher altitude, you cannot bank on that altitude to extend your descent distance. You plan from that 300 feet per minute ceiling, and that's your conservative baseline. Let me tie this together with the figures I have here. shows the obstacle clearance climb profile when there is no cloud, and shows the same profile when there is cloud. These illustrate how the climb gradient and obstacle clearance work in practice — the cloud case changes the profile because you have to account for the cloud base. But the compliance rules we just covered apply to the en route descent range calculation, and they're the conservative constraints you must respect. So the key takeaway: you calculate your descent range and cruise range, plot a track that keeps an airfield within that total descent distance, and you do it using the 300 feet per minute altitude cap and the 0.5% gradient penalty. That's how you prove compliance with the regulation.