Performance/Power
Thread Starter
Joined: Jan 2011
Posts: 2
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From: Manchester
Performance/Power
Hi, nervous flyer here. I have a question about aircraft performance, hoping someone with professional credentials could put my mind at ease.
As a youngster in the late 80s, early 90s I flew a lot with family to Mediterranean destinations for package holidays and it always seemed to be 757s or, once or twice, the L1011s with Caledonian (remember them?) Anyway, I loved those aircraft because they had such a tangible sense of power - they always seemed to go down the runway like the proverbial !!!! off a shovel, and unlike most pax I really enjoyed the loud engine noise because it sounded very reassuring.
After a few years without flying I recently had a couple of journeys on newer, smaller aircraft that were much less enjoyable. Climb seemed to take forever and on one occasion it seemed like a real struggle to get clear of some unpleasant weather.
But to the point: I have a flight coming up with easyjet on the A319. I've seen a few discussions online about the A319 being almost as heavy as the 320 with nothing like as much thrust, and of easyjet having to disembark a few passengers at high/hot airports to make sure they could get away alright. Now...this kind of thing makes me worry, because I've always been led to understand that any twin jet should be able to cope with the loss of one engine after v1, and fly safely on the other? But if the 319 when fully loaded at a warm airport is struggling on two, what happens if it goes down to one? Would you still be able to get a climb rate out of it? Is the maximum take-off weight calculated with a potential single engine scenario in mind?
I wish the 757 was still around
As a youngster in the late 80s, early 90s I flew a lot with family to Mediterranean destinations for package holidays and it always seemed to be 757s or, once or twice, the L1011s with Caledonian (remember them?) Anyway, I loved those aircraft because they had such a tangible sense of power - they always seemed to go down the runway like the proverbial !!!! off a shovel, and unlike most pax I really enjoyed the loud engine noise because it sounded very reassuring.
After a few years without flying I recently had a couple of journeys on newer, smaller aircraft that were much less enjoyable. Climb seemed to take forever and on one occasion it seemed like a real struggle to get clear of some unpleasant weather.
But to the point: I have a flight coming up with easyjet on the A319. I've seen a few discussions online about the A319 being almost as heavy as the 320 with nothing like as much thrust, and of easyjet having to disembark a few passengers at high/hot airports to make sure they could get away alright. Now...this kind of thing makes me worry, because I've always been led to understand that any twin jet should be able to cope with the loss of one engine after v1, and fly safely on the other? But if the 319 when fully loaded at a warm airport is struggling on two, what happens if it goes down to one? Would you still be able to get a climb rate out of it? Is the maximum take-off weight calculated with a potential single engine scenario in mind?
I wish the 757 was still around
Joined: Apr 2007
Posts: 58
Likes: 3
From: Aberdeen
Firstly, I'm not a professional so I could be talking rubbish but...
Imagine you have a Ferrari. You can get up to speed really quickly by gunning the engine and flooring it, but you'll use more fuel and there will be more stress on the engine.
Alternatively, you could accelerate at a sensible speed and use less fuel and put less stress on the engine.
It might be the same with planes, and in today's economic climate then saving cash is the name of the game!
Imagine you have a Ferrari. You can get up to speed really quickly by gunning the engine and flooring it, but you'll use more fuel and there will be more stress on the engine.
Alternatively, you could accelerate at a sensible speed and use less fuel and put less stress on the engine.
It might be the same with planes, and in today's economic climate then saving cash is the name of the game!
Joined: Oct 2005
Posts: 3,218
Likes: 2
From: USA
Hulmerist,
I don't fly the A319, so I can't speak to that particular design. However, all transport category aircraft must meet minimum performance standards with a loss of power. The A319 is no different.
Some airplanes may be perceived as flying higher, faster, or accelerating on the runway faster. This has no bearing on their ability to meet minimum performance standards, however.
Part of conducting a flight is ensuring that the aircraft is loaded such that it can meet the performance standards. The amount of fuel that must be carried is determined based on weight, temperature, distance, runway lengths, alternate airports, expected delays, etc. The amount of weight that can be carried is limited by runway lengths, temperature, and available fuel. When a flight is put together, airlines do not simply load the airplane with as much as it can possibly carry, and take off. Every single flight is closely examined, planned, and loaded for the necessary performance to conduct the flight safely.
V1 is a speed that is used on the runway, and it divides the takeoff into two regimes: before V1 the takeoff may be rejected, and the airplane may stop in the remaining runway. After V1, this is no longer possible, and the airplane must go fly.
After V1, a second speed becomes very important, and this is V2. Takeoff safety speed, or V2, is important for several reasons, not the least of which is that it assures positive aircraft control. Just as importantly, however, takeoff safety speed is also applied to the aircraft performance just after takeoff with an engine-out, and it provides the best available aircraft capability. From the time the gear is retracted until the airplane reaches a safe altitude or an initial level-off altitude, the airplane is in a regime called the "second-segment climb," and it's during this critical period that the most important climb criteria must be met.
What this means for you is that the A319 must take off at a weight that will allow it, given the runway length, temperature, and other factors, to climb away with an engine failure using the same minimum performance that the 757 had. While the 757 may have had greater capability than that minimum, it still had to be loaded and flown always capable of meeting minimum climb requirements. So must the A319.
Sometimes takeoffs are performed using "reduced thrust," or what's sometimes referred to as "flex thrust." This means taking off with less thrust than the maximum available. This creates economic savings, but is also safety-related because it puts less stress on the engine, uses lower temperatures, increases parts longevity and reliability and because it's always calculated to meet all of the minimum performance requirements. Airplanes may be capable of doing more, but it's the minimum criteria to which we look; the airplane, whatever airplane it is, must always be capable of meeting these minimum requirements. The minimum requirements vary with the airport and obstacles and the type of departure. What this means for you is that every time we takeoff, we calculate the takeoff capability and performance tailored to that day, on that runway, for that departure, for that flight.
Every flight on which you ride has this done. Every time the airplane takes off and lands, whatever airplane it is, the company and the crew have calculated and confirmed the capability of the airplane to perform under the conditions that exist at the time of takeoff. Not only performance with all engines running, but with an engine shut down, as well. Obstacles around the runway are taken into account, including temporary towers or other obstacles that may only be in the area for a short time. Terrain is factored in, as are minimum climb gradients for the airplane and phase of flight, for the departure procedure, and that may be required by air traffic control.
All of this is part of the preflight planning. When we prepare to push back to go fly, we look very closely at all the current information regarding the airport, the airplane, the weather, and the flight. We take into account any inoperative equipment, any notices to airman showing obstacles, runway shortening, intersection departures, or departure procedures. We note our weight and confirm it from the flight plan, the weight and balance calculations sheet, and from the takeoff and landing data card (TOLD card). We brief these items, and compare them together as a crew before we depart. We note the amount of runway available after stopping if we must reject the takeoff, and we brief how and why we'll reject the takeoff or keep going.
We brief the reasons that the takeoff may be rejected and the reasons why it may be continued. We discuss the performance we can expect after takeoff, and the actions we will take. We have level-off altitudes that are part of our emergency procedures, and we brief those, as well as any special "turn-procedures" that we may use while departing with a power loss. All of this is pre-briefed and confirmed in the cockpit before we takeoff. On our checklist is a requirement for confirmation of these items again, verbally by all crew members, while entering the runway for takeoff. Everyone has to agree, as must computerized programs, performance charts, and the dispatcher.
Every aspect of the takeoff is closely examined. A contaminated or wet runway changes the stopping distance, the weight we can takeoff, and the power settings we can use. Windshear reported in the area affects our power setting and flap settings. Icing conditions affect our takeoff, as do numerous other factors. Each is meticulously taken into account when we plan for the takeoff, and when we perform the takeoff. The speeds are called-out loudly, and confirmed. Instrument indications are compared across the cockpit as part of those confirmations so that everyone is on the same page, seeing the same data, and communicating.
From the passenger perspective, I fully understand your concern about taking off in an airplane that might be perceived as "under powered."
From the pilot perspective, I hope you can understand my concern: if anything goes wrong, I'm the first one to the scene of the crash.
With that firmly in mind, you can bet that I take the performance capability of the airplane extremely seriously. As the one at the front of the airplane, you can rest assured that I take nothing for granted, double check everything, and take great pains to ensure both my safety, and yours. After all, you want to make this flight safely, and I want to make it safely and the next, and the next, and the next. After that, I want to go home to see my family, and I can only do that if I treat each flight as it's the most important even in the world. It is; because if I don't make it so, there won't be any others for me. I take your safety as seriously as my own, as does each crew member who sits in the cockpit ahead of you.
You're in good hands.
I don't fly the A319, so I can't speak to that particular design. However, all transport category aircraft must meet minimum performance standards with a loss of power. The A319 is no different.
Some airplanes may be perceived as flying higher, faster, or accelerating on the runway faster. This has no bearing on their ability to meet minimum performance standards, however.
Part of conducting a flight is ensuring that the aircraft is loaded such that it can meet the performance standards. The amount of fuel that must be carried is determined based on weight, temperature, distance, runway lengths, alternate airports, expected delays, etc. The amount of weight that can be carried is limited by runway lengths, temperature, and available fuel. When a flight is put together, airlines do not simply load the airplane with as much as it can possibly carry, and take off. Every single flight is closely examined, planned, and loaded for the necessary performance to conduct the flight safely.
V1 is a speed that is used on the runway, and it divides the takeoff into two regimes: before V1 the takeoff may be rejected, and the airplane may stop in the remaining runway. After V1, this is no longer possible, and the airplane must go fly.
After V1, a second speed becomes very important, and this is V2. Takeoff safety speed, or V2, is important for several reasons, not the least of which is that it assures positive aircraft control. Just as importantly, however, takeoff safety speed is also applied to the aircraft performance just after takeoff with an engine-out, and it provides the best available aircraft capability. From the time the gear is retracted until the airplane reaches a safe altitude or an initial level-off altitude, the airplane is in a regime called the "second-segment climb," and it's during this critical period that the most important climb criteria must be met.
What this means for you is that the A319 must take off at a weight that will allow it, given the runway length, temperature, and other factors, to climb away with an engine failure using the same minimum performance that the 757 had. While the 757 may have had greater capability than that minimum, it still had to be loaded and flown always capable of meeting minimum climb requirements. So must the A319.
Sometimes takeoffs are performed using "reduced thrust," or what's sometimes referred to as "flex thrust." This means taking off with less thrust than the maximum available. This creates economic savings, but is also safety-related because it puts less stress on the engine, uses lower temperatures, increases parts longevity and reliability and because it's always calculated to meet all of the minimum performance requirements. Airplanes may be capable of doing more, but it's the minimum criteria to which we look; the airplane, whatever airplane it is, must always be capable of meeting these minimum requirements. The minimum requirements vary with the airport and obstacles and the type of departure. What this means for you is that every time we takeoff, we calculate the takeoff capability and performance tailored to that day, on that runway, for that departure, for that flight.
Every flight on which you ride has this done. Every time the airplane takes off and lands, whatever airplane it is, the company and the crew have calculated and confirmed the capability of the airplane to perform under the conditions that exist at the time of takeoff. Not only performance with all engines running, but with an engine shut down, as well. Obstacles around the runway are taken into account, including temporary towers or other obstacles that may only be in the area for a short time. Terrain is factored in, as are minimum climb gradients for the airplane and phase of flight, for the departure procedure, and that may be required by air traffic control.
All of this is part of the preflight planning. When we prepare to push back to go fly, we look very closely at all the current information regarding the airport, the airplane, the weather, and the flight. We take into account any inoperative equipment, any notices to airman showing obstacles, runway shortening, intersection departures, or departure procedures. We note our weight and confirm it from the flight plan, the weight and balance calculations sheet, and from the takeoff and landing data card (TOLD card). We brief these items, and compare them together as a crew before we depart. We note the amount of runway available after stopping if we must reject the takeoff, and we brief how and why we'll reject the takeoff or keep going.
We brief the reasons that the takeoff may be rejected and the reasons why it may be continued. We discuss the performance we can expect after takeoff, and the actions we will take. We have level-off altitudes that are part of our emergency procedures, and we brief those, as well as any special "turn-procedures" that we may use while departing with a power loss. All of this is pre-briefed and confirmed in the cockpit before we takeoff. On our checklist is a requirement for confirmation of these items again, verbally by all crew members, while entering the runway for takeoff. Everyone has to agree, as must computerized programs, performance charts, and the dispatcher.
Every aspect of the takeoff is closely examined. A contaminated or wet runway changes the stopping distance, the weight we can takeoff, and the power settings we can use. Windshear reported in the area affects our power setting and flap settings. Icing conditions affect our takeoff, as do numerous other factors. Each is meticulously taken into account when we plan for the takeoff, and when we perform the takeoff. The speeds are called-out loudly, and confirmed. Instrument indications are compared across the cockpit as part of those confirmations so that everyone is on the same page, seeing the same data, and communicating.
From the passenger perspective, I fully understand your concern about taking off in an airplane that might be perceived as "under powered."
From the pilot perspective, I hope you can understand my concern: if anything goes wrong, I'm the first one to the scene of the crash.
With that firmly in mind, you can bet that I take the performance capability of the airplane extremely seriously. As the one at the front of the airplane, you can rest assured that I take nothing for granted, double check everything, and take great pains to ensure both my safety, and yours. After all, you want to make this flight safely, and I want to make it safely and the next, and the next, and the next. After that, I want to go home to see my family, and I can only do that if I treat each flight as it's the most important even in the world. It is; because if I don't make it so, there won't be any others for me. I take your safety as seriously as my own, as does each crew member who sits in the cockpit ahead of you.
You're in good hands.
Thread Starter
Joined: Jan 2011
Posts: 2
Likes: 0
From: Manchester
Wow, SNS3Guppy, thank you so much for taking the time to give such a thorough response. It is actually very reassuring to read those words and I appreciate it because now I will feel a little bit more comfortable stepping aboard my flight.
I guess this is the key point isn't it:
ie. all aircraft essentially have the same minimum performance capability even if some have more than others on top of that?
I guess when I think about it logically that's the only way it could be, and of course pilots want to get home in one piece just as much as the rest of us. So, yeah, in one respect I recognise how silly a concern it probably is to have. But it's just that...when you hear a lot of chatter about this aircraft or that aircraft (usually airbus) being "underpowered" and stuff about 340-300s taking forever to get airborne or 319s having pax offloaded, it creates the impression that they're struggling to fly at all and it just sort of makes you mentally compare different aircraft types against one another...which I guess is a misleading mental exercise because what matters is how they compare to the minimum performance standards (compared to which they're all essentially the same), as you point out.
I'm right in thinking that some aircraft do use their "extra" performance capability to climb more quickly, though, right? It could be my memory playing tricks on me, but it really seems like there's a discernible difference between the rate of climb in the 757s I used to fly on as a kid and the aircraft I've been on more recently. Obviously, as you said, each flight is unique and there are a lot of other determining factors, but in general it seemed the 757 was something of a rocket.
Incidentally, last time I was at my local airport, Manchester, I saw a 747-400 from Virgin Atlantic, which I believe was empty and being flown down to Gatwick for positioning, perform a staggeringly short take off and steep climb away. I was astonished at how quickly it got airborne, I'd never seen anything like it before.
Anyway, thanks again for your explanation, sir - more knowledge definitely = less fear.
Oh and The_Steed:
...is as close as I'm going to get, unfortunately.
I guess this is the key point isn't it:
A319 must take off at a weight that will allow it, given the runway length, temperature, and other factors, to climb away with an engine failure using the same minimum performance that the 757 had. While the 757 may have had greater capability than that minimum, it still had to be loaded and flown always capable of meeting minimum climb requirements.
I guess when I think about it logically that's the only way it could be, and of course pilots want to get home in one piece just as much as the rest of us. So, yeah, in one respect I recognise how silly a concern it probably is to have. But it's just that...when you hear a lot of chatter about this aircraft or that aircraft (usually airbus) being "underpowered" and stuff about 340-300s taking forever to get airborne or 319s having pax offloaded, it creates the impression that they're struggling to fly at all and it just sort of makes you mentally compare different aircraft types against one another...which I guess is a misleading mental exercise because what matters is how they compare to the minimum performance standards (compared to which they're all essentially the same), as you point out.
I'm right in thinking that some aircraft do use their "extra" performance capability to climb more quickly, though, right? It could be my memory playing tricks on me, but it really seems like there's a discernible difference between the rate of climb in the 757s I used to fly on as a kid and the aircraft I've been on more recently. Obviously, as you said, each flight is unique and there are a lot of other determining factors, but in general it seemed the 757 was something of a rocket.
Incidentally, last time I was at my local airport, Manchester, I saw a 747-400 from Virgin Atlantic, which I believe was empty and being flown down to Gatwick for positioning, perform a staggeringly short take off and steep climb away. I was astonished at how quickly it got airborne, I'd never seen anything like it before.
Anyway, thanks again for your explanation, sir - more knowledge definitely = less fear.
Oh and The_Steed:
Imagine you have a Ferrari.
Joined: Oct 2005
Posts: 3,218
Likes: 2
From: USA
ie. all aircraft essentially have the same minimum performance capability even if some have more than others on top of that?
I'm right in thinking that some aircraft do use their "extra" performance capability to climb more quickly, though, right?
That said, where a lot of extra performance isn't necessary on a given day, reduced thrust operations are fairly standard.
Joined: Jul 2007
Posts: 741
Likes: 7
From: Auckland, NZ
I'm not at all a professional, but it depends a bit on how long ago your childhood was. I think that when oil was cheap and airfares high, airlines used take-off power on take off. As commercial and cost pressures increased, they got a lot more clever about using enough power to be safe, but not wasting fuel or engine life.
I remember flying out of Canberra on DC-9s in the '70s, and that was exhilarating or, in my case, terrifying--almost as much so as a winch launch in a glider. 727s seemed much more sedate.
I remember flying out of Canberra on DC-9s in the '70s, and that was exhilarating or, in my case, terrifying--almost as much so as a winch launch in a glider. 727s seemed much more sedate.
Joined: Oct 2009
Posts: 543
Likes: 15
From: North West UK
I have flown two very contrasting flights on an A340-600 as well as many others - all four hour flights.
The first was when the plane was light on passengers and presumably luggage. It appeared to trundle down the runway at barely faster than taxiing speed before a gentle lift into the air. I was amazed we even got more than 1ft off the ground we appeared to be going so slowly.
The second was a similar flight, but the plane was full to bursting. We fairly raced down the runway like in days of old.
I am here to tell the tale of both flights!
The first was when the plane was light on passengers and presumably luggage. It appeared to trundle down the runway at barely faster than taxiing speed before a gentle lift into the air. I was amazed we even got more than 1ft off the ground we appeared to be going so slowly.
The second was a similar flight, but the plane was full to bursting. We fairly raced down the runway like in days of old.
I am here to tell the tale of both flights!
Joined: Feb 2005
Posts: 4,581
Likes: 0
From: flyover country USA
Bear in mind that if a 3-engine aircraft loses one, it's a 33% loss in thrust. If a twin loses one, it's a 50% loss. Considering that both aircraft must be able to perform safely in this condition, the twin is relatively OVERPOWERED when both engines are running.
This is even more true when comparing a twin to a 4-engine ship.
This is even more true when comparing a twin to a 4-engine ship.
Joined: Feb 2005
Posts: 4,581
Likes: 0
From: flyover country USA
Espada III:
Were both flights from the same runway? If the first flight was from a shorter runway, the captain probably used more of his available thrust; if the second flight was from a longer runway, not so much thrust was required.
There are many other variables too - you don't know how much excess "tanker" fuel (= more weight) was carried.
Were both flights from the same runway? If the first flight was from a shorter runway, the captain probably used more of his available thrust; if the second flight was from a longer runway, not so much thrust was required.
There are many other variables too - you don't know how much excess "tanker" fuel (= more weight) was carried.
