Aircraft Performance and Runway Essentials

Are you studying for your A to PL exams? Do you need a little bit of extra help with performance? Well, come with me as we break down this big subject into little bite-sized chunks. Hi, I'm Grant and welcome to the first in a new series all about performance. It's important we understand how our aircraft are going to perform on any given day so that we know if we'll be able to make it in and out of airports safely. In this first class we're going to be taking a look at some overall performance concepts as well as taking a look at some dimensions and characteristics of a typical runway. Before we get started looking at graphs and calculating speeds we need to get some basics down first. First of all why do we study performance? Well we need to know how our aircraft is going to act in certain situations. If we didn't know how much distance we needed for takeoff before setting takeoff power. then we might run out of runway before we get airborne. So it's important that we do this before we start rolling down the runway. Aircraft generally these days fall into one of two categories. You get sort of big jets for and turboprops for transport and you get smaller things as well for a bit more small flights really. As we can see we have a multi-engine jet aircraft. That's anything. aircraft that you would see at a big airport falls into this Class A categorization and that means that we've got to achieve certain performance standards which are set out in a document called CS25 certification specification 25 I think it stands for. For multi-engine turbo props it depends on the size of it what class we need to fall into so for big ones like a dash 8 you would use Class A but for smaller ones With nine or less passenger seats or weighing 5,700 kilograms or less maximum takeoff mass, then we fall into class B. Class B is set out in a similar document to class A in CS23, and the performance standards are a bit more lenient. They're a bit more relaxed than they are for class A. There's also a third column here for multi-engine propeller. driven aircraft. You can see that for small ones with nine or less passenger seats it's class B as well but then for larger ones there's a class C certification and that's not really used anymore. That's for things that were older sort of the 50s the 60s that sort of era and things like a DC-3 that sort of era of aircraft but class C you very rarely are in service anymore. So the ATPLs don't actually cover them but there is a third class of performance that you might have to know in the exam. There are various things that we want to calculate our performance for which we'll see a lot more of as we move through this series such as maximum takeoff weights, takeoff distances, landing distances, landing weights, steepness of climb, max endurance just to name a few. But they all have three types of performance within that type. We've got measured performance, gross performance and net performance. So starting off with measured performance, that's the performance data that the aircraft has achieved before it has entered commercial service and it's physically measured during a flight test by test pilots. All of the phases of flight are covered multiple times and an average is taken to show us the average measured performance for different characteristics. This graph here for example, shows the measured after takeoff single engine climb performance for a brand new Airbus A370 aircraft that we've just invented and we're trying to get certified. There are loads of lines but the average line is about here and that is the measured performance flown by test pilots. Unfortunately we're not all test pilots flying brand new A370s. Test pilots are highly skilled pilots that are used to flying the aircraft in unusual situations such as single engine which is what we're looking at here. We therefore need to find the average performance for the average plane by the average pilot. This is what we call gross performance. This is the average performance achieved by a range of or fleet of aircraft by the average pilot. It is useful data as it shows us how the aircraft should perform on average and it is worse than the measured performance as this is an average as well, it means that half the time the A370 will perform better than this. and half the time it will perform a little bit worse than this. For the single engine climb, the shallower line is obviously worse performance. We want to climb up a bit better. But if we were in descent, maybe the steeper line would be the worst performance because we don't want to descend or glide. We don't want to fall out of the sky. We want to glide a bit better, for instance. So because gross performance is an average, we normally apply a safety factor to gross performance. to account for some of these below average performances that we might expect. After this safety factor is applied we get net performance which will be a lot worse or slightly worse sorry than the gross performance figures. This net performance figure is then used to determine the maximum values for weights for example. In this example we would use the net performance line to see if we can clear the obstacles after takeoff. So say if there was an obstacle in here like this, like a mountain, we know that we'd be able to achieve it with our net performance and the gross and the measured would be sufficient as well. This means that we can add weight to the aircraft up to the point that the one engine single engine climb after takeoff of the A370 will achieve this net performance line. This is something we'll get into a bit more later on in the series but that's the basic kind of idea behind performance in general. We need to achieve the average performance for the average pilot on the average aircraft in a fleet with a safety factor applied to make the net performance. The size of the safety factor sort of varies depending on how variable the performance data is and the probability of an event happening. It's kind of complicated to explain. But we'll see throughout the course that it doesn't necessarily matter why it is the size that it is, but it's more important that we just apply the correct safety factor to the correct stage of flight. We need to know our aircraft's takeoff and landing distances in order to tell if we can land at an airport or not. Some things are obvious, such as an A380 being unable to land in a grass strip beside a farm. or a Cessna 172 being able to land on a 3000 meter long runway. There are some, well a lot more, borderline cases though that may impose limits on how heavy we can be on takeoff or landing. And we need to compare our achievable net performance versus the characteristics of the runway and the surrounding area. Take for instance an A380 at a short runway may only be able to take x amount of tons of fuel and passengers. because if it was fully loaded it wouldn't be able to achieve sufficient net climb gradient single engine to clear all of the surrounding terrain. This is why we need to be able to compare our calculated distances versus the runway's actual available distances that we have. There's no point trying to land at an airport if we need 2000 meters of runway for instance and the runway is only 1800 meters long. So runways look something a little bit like this. So this white line here is called the runway threshold. This is where the aircraft is strong enough to support the aircraft on landing. The strength of the runway is calculated using a pavement classification number or a PCN and then you compare that PCN to the aircraft classification number. If the pavement classification number is larger than the aircraft classification number then you can maneuver the aircraft on that part of the runway or aerodrome. Some taxiways for instance may have a lower pavement classification number than your aircraft's classification number so you wouldn't be able to taxi on those taxiways you might have to take a different route around the airport. Sometimes we can have a displaced threshold where there's a part of the runway that is unusable if it's given these x's and the threshold starts from the usable portion where the PCN is larger than the ACN. If the weight of an aircraft can be supported but not on landing, only when taxiing, then you may see a displaced threshold with arrows pointing towards it. That means that you can taxi on this runway but you can't, this part of the runway, but you can't land on this part of the runway and you can be used for takeoff for instance. You could taxi all the way down here and then you've got a slightly longer runway for takeoff. A stopway is an area after the runway which is free from obstacles and at least the same width as the runway. The stopway is used for aircraft in case of a rejected high-speed takeoff, so it's not part of the runway in normal operations. This means that it doesn't It doesn't need to be as strong or as well maintained as the normal runway and it can break if needed as long as it stops the aircraft. It is normally marked by yellow chevrons and it can be combined with a displaced threshold like this. The takeoff run available or the TORA is the distance on the runway from the start of the surface that can support an aircraft to the end of the surface that can support the aircraft on the ground under normal conditions. This is a bit of a complicated way of saying it means any part of the runway we can taxi on. So we'll always include the distance between the two thresholds because if we can land on it then we can definitely taxi on it. It might include the area before a displaced threshold but only if the area is suitable for taxiing but it will always end on reaching a stopway. So in our example this part of the runway in here is our takeoff run available. And that's our TORA for runway 09 and for runway 27 it would actually be the same distance in this example. But you can have variance. Runways are numbered by rounding to the nearest 10 degrees of the magnetic direction and then taking away the last zero. So this runway direction might actually be 092 degrees magnetic but we just you know round it take the last number off. A clear way is an area that might be provided at the end of a torah in the takeoff distance. It is an area free of obstacles that could cause a hazard to aircraft once airborne and it extends out 75 meters either side of the extended runway center line and it goes out to the first solid or non-fragable non-breakable object it encounters but that matches out at a 50 percent distance of the torah. So if our torah was a thousand meters and the first solid object was 600 meters away, our clearway would only extend out to 500 meters. The clearway is only used for aircraft once they're actually airborne, so it can be over land or water and it can be overlaid on top of areas only used for the ground roll in an emergency such as a stopway, such as this case. The clearway slopes up vertically from the end of the torah at a 0.75 degree angle or 1.25% gradient until it reaches the nearest solid object that is at least taller than 0.9 meters that pokes through this imaginary plane. Or we continue sloping up until we reach 150% of the torus distance. So if we add our clear way to our torus, we get the takeoff distance available. Take... off distance available the TOTA. So the TOTA is either going to be the smaller of the TORA plus the clearway or 1.5 times the TORA. The ASDA is the distance on the runway from the start of the surface that can support an aircraft to the end of the surface that can support the aircraft in an emergency condition without risk of serious accident and I've just realized that I've labeled them wrong. The ASDA should be this one and the TODA should be this one. Hopefully that makes sense. So the ASDA is the tora plus the stopway and the TODA, the takeoff distance available, is the takeoff run available plus any clearway up to a maximum of 1.5 times the tora. That's brilliant. Oh well. If our stopway and our... sorry if our ASDA and our TODA are the same then we call it a balanced field and that makes the takeoff performance calculations a little bit easier because we only need one distance for takeoff and one distance for rejecting a takeoff. So aircraft are certified to fly following certain performance rules. So there's Class A, Class B and Class C. Class A covers all jet aircraft, multi-engine jet aircraft and it also covers turboprops that have more than 10 passenger seats. and weigh more than 5700 kilograms at their maximum takeoff mass. Class B is for turboprops that are smaller than this so it's nine or less passenger seats and less than 5700 kilograms maximum takeoff mass and any piston propeller aircraft of the same size. And then there's Class C which covers the large piston propeller aircraft not really seen today so not really covered in the HPLs. We classify all of our various performance characteristics into measured gross and net performance. Measured is measured. just out the factory flown by test pilots a brand new aircraft gross is average aircraft average pilot average day and 50% of the time we're gonna perform worse than that 50% we're gonna try we're actually going to perform better than that and if we apply a little bit of a safety factor to account for this 50% worse performance then we get the net performance and the size of the safety factor varies depending on various conditions which we'll see throughout the course. So runway dimension characteristics, I just talked about them but labelled them wrong, but this is also wrong? No, this is correct, this is correct. Okay, okay, so we've got runway 09, runway 27. A white line across indicates a threshold. It can be displaced. If it's displaced with little x's, that means you can't even taxi on that part with the X's. If there's little arrows you can taxi on it but you can't land on that part. Between the two thresholds is the safe part to land an aircraft and we calculate if it's safe by comparing the pavement classification number to the aircraft classification number and if the pavement is better than the aircraft then we can land and taxi on that. Well we can land. or taxi depending on what we need. The distance between the threshold or the part that we can taxi on to the opposite part that we can taxi on safely is called the TORA, the take-off run available. If we add on a stopway which is a part used for stopping aircraft in emergency we would then get the accelerate stop distance available, the ASDA. And if we add on a clearway, which is 75 meters either side, sloping up at 0.75 degrees or 1.25% until the nearest obstacle, which is larger than 0.9 meters, pokes through the plane of that clearway, then we would get the TORA plus the clearway would equal the TODA, the takeoff distance available. Hopefully that makes sense. The way of explaining a clear way is a bit convoluted. Think about it as a sloping plane up like that and if there's any obstacles that poke through that, that's where it ends and it goes out to a maximum distance of d torah times 1.5.

Are you studying for your A to PL exams? Do you need a little bit of extra help with performance? Well, come with me as we break down this big subject into little bite-sized chunks.

Hi, I'm Grant and welcome to the first in a new series all about performance. It's important we understand how our aircraft are going to perform on any given day so that we know if we'll be able to make it in and out of airports safely. In this first class we're going to be taking a look at some overall performance concepts as well as taking a look at some dimensions and characteristics of a typical runway.

Before we get started looking at graphs and calculating speeds we need to get some basics down first. First of all why do we study performance? Well we need to know how our aircraft is going to act in certain situations.

If we didn't know how much distance we needed for takeoff before setting takeoff power. then we might run out of runway before we get airborne. So it's important that we do this before we start rolling down the runway.

Aircraft generally these days fall into one of two categories. You get sort of big jets for and turboprops for transport and you get smaller things as well for a bit more small flights really. As we can see we have a multi-engine jet aircraft. That's anything.

aircraft that you would see at a big airport falls into this Class A categorization and that means that we've got to achieve certain performance standards which are set out in a document called CS25 certification specification 25 I think it stands for. For multi-engine turbo props it depends on the size of it what class we need to fall into so for big ones like a dash 8 you would use Class A but for smaller ones With nine or less passenger seats or weighing 5,700 kilograms or less maximum takeoff mass, then we fall into class B. Class B is set out in a similar document to class A in CS23, and the performance standards are a bit more lenient. They're a bit more relaxed than they are for class A. There's also a third column here for multi-engine propeller.

driven aircraft. You can see that for small ones with nine or less passenger seats it's class B as well but then for larger ones there's a class C certification and that's not really used anymore. That's for things that were older sort of the 50s the 60s that sort of era and things like a DC-3 that sort of era of aircraft but class C you very rarely are in service anymore.

So the ATPLs don't actually cover them but there is a third class of performance that you might have to know in the exam. There are various things that we want to calculate our performance for which we'll see a lot more of as we move through this series such as maximum takeoff weights, takeoff distances, landing distances, landing weights, steepness of climb, max endurance just to name a few. But they all have three types of performance within that type. We've got measured performance, gross performance and net performance.

So starting off with measured performance, that's the performance data that the aircraft has achieved before it has entered commercial service and it's physically measured during a flight test by test pilots. All of the phases of flight are covered multiple times and an average is taken to show us the average measured performance for different characteristics. This graph here for example, shows the measured after takeoff single engine climb performance for a brand new Airbus A370 aircraft that we've just invented and we're trying to get certified. There are loads of lines but the average line is about here and that is the measured performance flown by test pilots. Unfortunately we're not all test pilots flying brand new A370s.

Test pilots are highly skilled pilots that are used to flying the aircraft in unusual situations such as single engine which is what we're looking at here. We therefore need to find the average performance for the average plane by the average pilot. This is what we call gross performance.

This is the average performance achieved by a range of or fleet of aircraft by the average pilot. It is useful data as it shows us how the aircraft should perform on average and it is worse than the measured performance as this is an average as well, it means that half the time the A370 will perform better than this. and half the time it will perform a little bit worse than this.

For the single engine climb, the shallower line is obviously worse performance. We want to climb up a bit better. But if we were in descent, maybe the steeper line would be the worst performance because we don't want to descend or glide.

We don't want to fall out of the sky. We want to glide a bit better, for instance. So because gross performance is an average, we normally apply a safety factor to gross performance. to account for some of these below average performances that we might expect.

After this safety factor is applied we get net performance which will be a lot worse or slightly worse sorry than the gross performance figures. This net performance figure is then used to determine the maximum values for weights for example. In this example we would use the net performance line to see if we can clear the obstacles after takeoff.

So say if there was an obstacle in here like this, like a mountain, we know that we'd be able to achieve it with our net performance and the gross and the measured would be sufficient as well. This means that we can add weight to the aircraft up to the point that the one engine single engine climb after takeoff of the A370 will achieve this net performance line. This is something we'll get into a bit more later on in the series but that's the basic kind of idea behind performance in general.

We need to achieve the average performance for the average pilot on the average aircraft in a fleet with a safety factor applied to make the net performance. The size of the safety factor sort of varies depending on how variable the performance data is and the probability of an event happening. It's kind of complicated to explain.

But we'll see throughout the course that it doesn't necessarily matter why it is the size that it is, but it's more important that we just apply the correct safety factor to the correct stage of flight. We need to know our aircraft's takeoff and landing distances in order to tell if we can land at an airport or not. Some things are obvious, such as an A380 being unable to land in a grass strip beside a farm. or a Cessna 172 being able to land on a 3000 meter long runway.

There are some, well a lot more, borderline cases though that may impose limits on how heavy we can be on takeoff or landing. And we need to compare our achievable net performance versus the characteristics of the runway and the surrounding area. Take for instance an A380 at a short runway may only be able to take x amount of tons of fuel and passengers.

because if it was fully loaded it wouldn't be able to achieve sufficient net climb gradient single engine to clear all of the surrounding terrain. This is why we need to be able to compare our calculated distances versus the runway's actual available distances that we have. There's no point trying to land at an airport if we need 2000 meters of runway for instance and the runway is only 1800 meters long. So runways look something a little bit like this. So this white line here is called the runway threshold.

This is where the aircraft is strong enough to support the aircraft on landing. The strength of the runway is calculated using a pavement classification number or a PCN and then you compare that PCN to the aircraft classification number. If the pavement classification number is larger than the aircraft classification number then you can maneuver the aircraft on that part of the runway or aerodrome.

Some taxiways for instance may have a lower pavement classification number than your aircraft's classification number so you wouldn't be able to taxi on those taxiways you might have to take a different route around the airport. Sometimes we can have a displaced threshold where there's a part of the runway that is unusable if it's given these x's and the threshold starts from the usable portion where the PCN is larger than the ACN. If the weight of an aircraft can be supported but not on landing, only when taxiing, then you may see a displaced threshold with arrows pointing towards it.

That means that you can taxi on this runway but you can't, this part of the runway, but you can't land on this part of the runway and you can be used for takeoff for instance. You could taxi all the way down here and then you've got a slightly longer runway for takeoff. A stopway is an area after the runway which is free from obstacles and at least the same width as the runway. The stopway is used for aircraft in case of a rejected high-speed takeoff, so it's not part of the runway in normal operations. This means that it doesn't It doesn't need to be as strong or as well maintained as the normal runway and it can break if needed as long as it stops the aircraft.

It is normally marked by yellow chevrons and it can be combined with a displaced threshold like this. The takeoff run available or the TORA is the distance on the runway from the start of the surface that can support an aircraft to the end of the surface that can support the aircraft on the ground under normal conditions. This is a bit of a complicated way of saying it means any part of the runway we can taxi on. So we'll always include the distance between the two thresholds because if we can land on it then we can definitely taxi on it.

It might include the area before a displaced threshold but only if the area is suitable for taxiing but it will always end on reaching a stopway. So in our example this part of the runway in here is our takeoff run available. And that's our TORA for runway 09 and for runway 27 it would actually be the same distance in this example.

But you can have variance. Runways are numbered by rounding to the nearest 10 degrees of the magnetic direction and then taking away the last zero. So this runway direction might actually be 092 degrees magnetic but we just you know round it take the last number off. A clear way is an area that might be provided at the end of a torah in the takeoff distance.

It is an area free of obstacles that could cause a hazard to aircraft once airborne and it extends out 75 meters either side of the extended runway center line and it goes out to the first solid or non-fragable non-breakable object it encounters but that matches out at a 50 percent distance of the torah. So if our torah was a thousand meters and the first solid object was 600 meters away, our clearway would only extend out to 500 meters. The clearway is only used for aircraft once they're actually airborne, so it can be over land or water and it can be overlaid on top of areas only used for the ground roll in an emergency such as a stopway, such as this case. The clearway slopes up vertically from the end of the torah at a 0.75 degree angle or 1.25% gradient until it reaches the nearest solid object that is at least taller than 0.9 meters that pokes through this imaginary plane.

Or we continue sloping up until we reach 150% of the torus distance. So if we add our clear way to our torus, we get the takeoff distance available. Take...

off distance available the TOTA. So the TOTA is either going to be the smaller of the TORA plus the clearway or 1.5 times the TORA. The ASDA is the distance on the runway from the start of the surface that can support an aircraft to the end of the surface that can support the aircraft in an emergency condition without risk of serious accident and I've just realized that I've labeled them wrong.

The ASDA should be this one and the TODA should be this one. Hopefully that makes sense. So the ASDA is the tora plus the stopway and the TODA, the takeoff distance available, is the takeoff run available plus any clearway up to a maximum of 1.5 times the tora.

That's brilliant. Oh well. If our stopway and our...

sorry if our ASDA and our TODA are the same then we call it a balanced field and that makes the takeoff performance calculations a little bit easier because we only need one distance for takeoff and one distance for rejecting a takeoff. So aircraft are certified to fly following certain performance rules. So there's Class A, Class B and Class C. Class A covers all jet aircraft, multi-engine jet aircraft and it also covers turboprops that have more than 10 passenger seats.

and weigh more than 5700 kilograms at their maximum takeoff mass. Class B is for turboprops that are smaller than this so it's nine or less passenger seats and less than 5700 kilograms maximum takeoff mass and any piston propeller aircraft of the same size. And then there's Class C which covers the large piston propeller aircraft not really seen today so not really covered in the HPLs. We classify all of our various performance characteristics into measured gross and net performance. Measured is measured.

just out the factory flown by test pilots a brand new aircraft gross is average aircraft average pilot average day and 50% of the time we're gonna perform worse than that 50% we're gonna try we're actually going to perform better than that and if we apply a little bit of a safety factor to account for this 50% worse performance then we get the net performance and the size of the safety factor varies depending on various conditions which we'll see throughout the course. So runway dimension characteristics, I just talked about them but labelled them wrong, but this is also wrong? No, this is correct, this is correct. Okay, okay, so we've got runway 09, runway 27. A white line across indicates a threshold. It can be displaced.

If it's displaced with little x's, that means you can't even taxi on that part with the X's. If there's little arrows you can taxi on it but you can't land on that part. Between the two thresholds is the safe part to land an aircraft and we calculate if it's safe by comparing the pavement classification number to the aircraft classification number and if the pavement is better than the aircraft then we can land and taxi on that. Well we can land. or taxi depending on what we need.

The distance between the threshold or the part that we can taxi on to the opposite part that we can taxi on safely is called the TORA, the take-off run available. If we add on a stopway which is a part used for stopping aircraft in emergency we would then get the accelerate stop distance available, the ASDA. And if we add on a clearway, which is 75 meters either side, sloping up at 0.75 degrees or 1.25% until the nearest obstacle, which is larger than 0.9 meters, pokes through the plane of that clearway, then we would get the TORA plus the clearway would equal the TODA, the takeoff distance available.

Hopefully that makes sense. The way of explaining a clear way is a bit convoluted. Think about it as a sloping plane up like that and if there's any obstacles that poke through that, that's where it ends and it goes out to a maximum distance of d torah times 1.5.

Transcript for:Aircraft Performance and Runway Essentials

Transcript for:
Aircraft Performance and Runway Essentials