Class A Aircraft - Take-off — Page 372, Lesson 454

Right, let's get into Class A take-off performance. This is where the real depth of performance engineering starts, so I want to set the scene properly. First, the specimen aeroplane we use for all Class A performance work is the Boeing 737-400 series. And just to anchor you, let's re-establish the definition of a Class A aeroplane: it's any multi-engine jet, or any turbo-propeller aeroplane with a mass of more than 5700 kilograms, OR 10 seats or more. So if it's a jet with more than one engine, it's Class A. If it's a turboprop and it's heavy or carries ten or more people, it's Class A. Now, why do these aeroplanes get such special treatment? Because of their high passenger capacity and high speed, they must have the highest safety standards. And those standards are enforced in two distinct ways. Firstly, by the certification requirements, which are laid down in CS-25. That's the certification specification for large aeroplanes — it's how the aircraft type gets its certificate in the first place. Secondly, by the operational requirements, which are laid down in EU-OPS 1. That's how the operator — the airline — is allowed to use that certified aircraft in day-to-day service. Now here's the crucial difference, and I want you to really lock this in because it changes everything about how we assess performance. The operational requirements have one unique detail for Class A aeroplanes that is very different from Class B. For Class A aeroplanes, engine failure must be considered for ALL stages of flight. Think about that — every single phase, from the moment we start the take-off roll to the moment we shut down at the gate. Compare that to multi-engine Class B aeroplanes, where engine failure was not assumed below 300 feet. So for a Class B, below 300 feet on take-off, we didn't have to plan for an engine failure. For Class A, we do — at every stage. That single assumption adds an extra dimension to understanding and assessment of the aeroplane's performance. It means a lot of new terms and concepts are going to be introduced, and you'll need to become very familiar with them before you can fully appreciate Class A performance. We'll get to those shortly. But before we detail those new terms, let's examine what the operational requirements actually are. EU-OPS 1.490 states that an operator must ensure the take-off mass does not exceed the maximum take-off mass as published in the aeroplane flight manual. So the flight manual — the AFM — publishes a maximum take-off mass, and the operator must never plan a take-off above that figure. And here's the key part: when calculating that maximum take-off mass, two distance constraints must be satisfied. The accelerate-stop distance must not exceed the accelerate-stop distance available. And the take-off distance must not exceed the take-off distance available. Let me unpack those terms because they're fundamental. Accelerate-stop distance — that's the distance required to accelerate to a certain speed and then, if we decide to abort, stop the aeroplane. It's the "go or stop" decision distance. The accelerate-stop distance available is the physical runway length we have to do that — the declared distance available for that manoeuvre. So the requirement is: what we need must not exceed what we have. Similarly, take-off distance — that's the distance required to get airborne and reach a specified height. And take-off distance available is the runway length declared available for that. Again, required must not exceed available. So the whole regulatory framework for Class A take-off is built on this: we calculate a maximum take-off mass, and that mass is limited by ensuring our required distances never exceed the available distances. That's the foundation. Now let's look at the figure that illustrates this — it shows the gross take-off distance multiplied by 1.25 must not exceed the TORA. TORA is Take-Off Run Available — the runway length declared available for the ground run during take-off. So there's a safety factor built in: the gross take-off distance, multiplied by 1.25, must fit within the TORA. That's a hard regulatory limit. So to summarise where we are: Class A means engine failure is assumed at all stages. The operational requirement, EU-OPS 1.490, caps take-off mass at the AFM value, and that mass must satisfy both the accelerate-stop distance and take-off distance constraints against their available counterparts. And we've got that 1.25 factor on the gross take-off distance against TORA. That's the regulatory skeleton. Now we're ready to build the flesh on it — the new terms and concepts that come from assuming engine failure at every stage.