Multi-engine Class B - Landing — Page 368, Lesson 442

Let's start with the landing climb requirement for a multi-engine Class B aeroplane, because this is where the certification rules get really specific. The rule is this: with the critical engine inoperative, the gradient of climb must not be less than 0.75% at an altitude of 1500 feet above the landing surface. Let me unpack that. The critical engine is the one whose failure is most adverse to performance — the one that, if it fails, hurts you the most. And the gradient of climb is the ratio of vertical height gained to horizontal distance travelled, expressed as a percentage. So 0.75% means for every 100 feet you travel forward, you climb just three-quarters of a foot. It's a very shallow climb, and that's deliberate. Now, this gradient must be achieved under a very specific set of conditions. The critical engine is inoperative and its propeller is feathered — that means the blades are turned edge-on to the airflow to reduce drag. The live engine is set at maximum continuous power. The landing gear, which we also call the undercarriage, is retracted. The flaps are retracted. And the climb speed must not be less than 1.2 times VS1. VS1 is the stalling speed in a specified configuration, so 1.2VS1 is a safety margin above the stall. Notice something important here. For this climb demonstration, both the undercarriage and the flaps are assumed to be retracted — the aeroplane is in a clean configuration. Why? Because the failure of the critical engine results in an approximate 75% loss of climb gradient. That's a huge loss. If the regulators set the required gradient too high, the aeroplane couldn't meet it, and the only way to comply would be to reduce the weight — which would cut into the payload the aeroplane can carry. So the requirement is set low, at 0.75%, and the configuration is kept clean, to protect the operational capability of the aeroplane. The term used to describe the maximum mass that can be carried and still attain this minimum gradient is called the Landing Climb Limit Mass. That's your limiting weight for this condition. One important qualification: these climb gradient requirements are specific to aeroplanes in the normal, utility, and aerobatic category of more than 2722 kg. So they only represent a portion of the requirements for multi-engine Class B aeroplanes — not the whole picture. Now, there's a practical side to this. An example of a landing climb performance graph is on page 19 of section 3 in CAP 698. That graph is for the baulked landing — in other words, an all-engine full-power go-around. But here's the catch: the graph only gives you a rate of climb, not a gradient. So to know if the aeroplane is achieving the minimum required gradient of 2.5%, you must convert the rate of climb into a gradient. An example of that calculation is shown at the bottom of page 18 of section 3 in CAP 698. So you have two different gradients in play: the 0.75% for the critical-engine-inoperative case, and the 2.5% for the all-engine baulked landing case. Let me now move to the landing distance requirements, which come from EU-OPS 1.550. For multi-engine Class B aircraft, these are the same as for single-engine aircraft, which you'd have seen in Chapter 10. You can find them in CAP 698 in the middle of page 17 of section 3. EU-OPS 1.550 states that an operator must ensure that the landing mass of the aeroplane, for the estimated time of arrival, allows a full-stop landing from 50 feet above the threshold within 70% of the landing distance available at the destination aerodrome and at any alternate aerodrome. Let me break that down. The landing mass is the weight of the aeroplane at the time of landing, and you must check it for the estimated time of arrival — the time you expect to arrive. The aeroplane must be able to come to a full stop, having crossed the threshold at 50 feet, within 70% of the landing distance available. The landing distance available is the length of runway declared available for landing. So you only get to use 70% of that runway for your actual stopping distance. The factor to use for such calculations is 1.43. That's the reciprocal of 0.7 — you divide your required landing distance by 0.7, or multiply by 1.43, to find the minimum landing distance available you need. So the key numbers to remember: 0.75% gradient at 1500 feet with the critical engine out, 1.2VS1 minimum climb speed, the 2.5% gradient for the all-engine baulked landing, and the 70% landing distance factor with its 1.43 multiplier.