Forgive me for being a complete fetus in the aviation world, but I was hoping for some light on these topics.
1. Is there more than simply pushing the throttle to the desired power to takeoff, or anytime else? I thought you calculated how much thrust you'd need, and then you'd push the throttle to that level to takeoff. If the throttle does not directly equal power output at all times (which I think would be dumb), is there a setting that can allow for that to be the case?
2. How much flexibility do you have with power and climb rates? If you have a "lead foot", can you err on the side of faster acceleration and more power if you want? Can you use maximum power if you want, even if it's not required?
3. Are there any specific airports or runways that generally require maximum thrust and/or a steep climb rate at takeoff, so you'd know for sure planes would be operating full performance there?
4. If you wanted to, could you fly, or plan to fly, at near maximum climb rate for a significant portion of your ascent to cruising altitude? Who decides that?
5. At cruising altitude, are you always flying at your maximum cruising speed? If not, why not? If the reason is fuel, who cares? Do airlines keep track of which pilots have a heavy foot and which do not?
Thank you for this. I've done lots of reading and haven't been able to really figure these things out clearly. I appreciate it!
The following applies to airliners.
1. Yes there is a lot more than just pushing the thrust levers to the detent, but importantly it all comes before that action. Once you say "takeoff" and push the thrust levers up, all the calculations have already been done, which is why it seems deceptively simple.
A takeoff calculation is done (paper, ACARS to central computer, or EFB) based on weight, runway and environmental. This spits out thrust setting (derate, flex/assumed temp, or TOGA), v speeds and flap setting which are then entered in the FM. When the thrust levers are set to the appropriate detent, FADEC will set the demanded thrust level.
Manual thrust is always available. Sometimes it is the only thing available if autothrust is inop. For take-off, though, you'd always set it to either TOGA or derate/flex. It is the only way to ensure desired performance.
The thrust levers position is not directly proportional to thrust, because jet engine thrust is very far from linear to fuel flow (and thus mass flow). For the sake of the exercise, if we assume that thrust lever angle is proportional to fuel flow, the top 20% of thrust lever travel would probably give you more than 50% of the thrust variation.
2. Climb rates and thrust. Airliners typically climb at a fixed thrust setting, either max climb thrust or a derated climb thrust. By varying the speed, we can vary the climb angle and rate. For example if there is a minimum altitude close in, we would climb slower than normal, giving a steeper climb angle. It isn't quite as simple as just slowing down, though. Minimum speed, best angle of climb speed, and best rate of climb speed increase with altitude, so you have to be careful not to paint yourself into a corner, so to speak.
("Fixed thrust setting" isn't strictly true, because available thrust decreases with altitude, but FADEC handles that so it is transparent to the pilots.)
3. Certainly some airports will typically require higher thrust setting than others. Shorter runways and/or close in obstacles, require higher takeoff thrust settings. And some airports with very rough runway surfaces might have "minimum ground roll" calculation options that shortens the takeoff run. However, takeoff performance is calculated for every takeoff and varies widely. 20 tons weight more or less, or 10 knots of wind, will make a massive difference to performance numbers.
It isn't just thrust that varies. It is also flap setting. While on the 330 we typically use Flap 1, if the runway is short we might use flap 2 or even flap 3. In general, more flap gives a shorter takeoff roll, but worse initial climb performance.
4. In many places, climb restrictions, either charted or instructed by ATC, force tactical decisions on climb angle. We also often change climb rate to avoid triggering TCAS advisories, or to get above clouds that cause turbulence. Given no restrictions, we could choose to climb faster than "optimal", but since optimal is what the plane thinks is most efficient, that is what we should be doing. We work for a commercial operation, after all.
The saying for what to do in case we have a tight climb constraint goes "negotiate, decelerate, derate". First, negotiate with ATC to see if they can give you something less restrictive. If you can't, decelerate to increase climb angle. And if you can't do that either, remove the derate. Efficiency is key.
5. We almost never fly at max cruise speed. If we did, we would often find ourselves with too little fuel to get to the destination. The cruise speed on the day is dictated by the cost index, a number which represents the tradeoff between fuel and time. The lower the cost index, the less fuel we use and the slower we fly. However, slower means longer flight, meaning more time on the engines and airframe, more hours paid to the crew and so on. The cost index is set based on complex cost calculations on the day, and printed on the flight plan. We sometimes tactically deviate from the cost index, for example if we get a time constraint from ATC, but normally just stay on it.
Does the company keep track of cruise fuel consumption? Not at the captain by captain level, I think, but since fuel is the biggest cost we have, it is certainly a focus of attention. Again, we work for a commercial operation, so we take pride in being efficient.
Great replies, thank you! FYI, I am more interested in commercial airliners, the big boys.
Tell me pilots, does the throttle lever, with its settings at intervals with no change in between, going to a computer to decide, doesn't that take the fun away? I used to love the quote about racing car drivers, when someone would suggest their car was the fastest and that's why they won, that it's not because of that, "it's the driver in the driver's seat doing the driving." I personally hate how modern cars don't have a direct throttle hookup to the butterfly valve. You hit the gas and then a computer decides everything, from the gear to the gas... and usually it's not what I want. I drive a manual transmission from the 90s solely for those reasons. I know that piloting an a350 isn't a race, but you didn't sign up to be computer technicians, right? You signed up to fly airplanes. Yes, you're in "control", but you're not in control in the moments you would want to be. It seems like at least.
I want to clarify that when I was referring to being able to use full thrust whenever you wanted it, what I meant was, could you use maximum takeoff thrust even if conditions didn't require it? Just because you wanted to? And what about during the climb, or at altitude, can you still get the maximum takeoff thrust then? Could you climb for a period at maximum takeoff thrust if you wanted?
What if, for example, you saw there were a lot of plane spotters out watching you prepare to takeoff. Could you do a full power, steep climb out of there to give them a show? Thanks all.
I can only speak for myself but it does not take the fun away.
Jet engines are finicky beasts, and before FADEC a flight engineer was needed to take care of them. FADEC is magic and should be worshipped.
As airline pilots we have a duty to the bottom line. We can't just use TOGA just because we feel like it, because that would increase cost. That being said, safety is paramount, and if the conditions warrant it (e.g. windshear forecast) we could certainly choose to use all the performance available.
The climbout is based on the conditions on the day. We can't climb steeper than what will maintain the speed. Most climbs are done at a set thrust (typically derated but sometimes max).
You have to remember the purpose of what airline pilots do, and it is not doing "cool stuff" like max performance takeoffs all the time. By no means does this decrease job satisfaction. We take pride in an efficient operation. Pushing on time, solving dispatch problems, getting that rotation just right, managing the climb to meet a tight restriction, avoiding weather in order to give a more comfortable ride, managing the descent profile just so, touching down in the zone smoothly. These things all give us job satisfaction. Even managing a single-engine go around in the sim to perfection, with callouts and actions unhurried and confident, makes me smile.
..as a follow on, for FADEC implementations, do all the parameters need to be manually entered, like atmospheric conditions, aircraft weight, etc? Or are there sensors on the LG for weight/mass and weather sensors that feed the data directly into the FADEC?
"Manually", but not in the FM itself. Takeoff performance is calculated separately, which spits out performance figures. The inputs are weight, runway and environmentals. This used to be done paper (before my time). A few years ago we entered data into an ACARS form, sent that off, and a few minutes later the printer spat out the figures calculated by a computer system located somewhere. Now we do it in the Airbus FlySmart software on our EFBs. You get the thrust setting, config (flap setting) and V speeds, which you then enter in the FM.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo