haha ok I like a challenge.....going for lunch in a bit tho so if I don't reply straight away I'll be back in around 15mins. Oh and you can stop asking for permission to ask a question haha, just ask!
Scary moment on a flight today
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haha ok I like a challenge.....going for lunch in a bit tho so if I don't reply straight away I'll be back in around 15mins. Oh and you can stop asking for permission to ask a question haha, just ask!
Assumed temperature t/o.
Have you any idea of the parameters of the calculations the FMC makes when you enter an assumed temperature with regards to the de-rate? I've been trying to work out where the figures come from, and been failing quite miserably.
Have you any idea of the parameters of the calculations the FMC makes when you enter an assumed temperature with regards to the de-rate? I've been trying to work out where the figures come from, and been failing quite miserably.
Well its all to do with air density and hence thrust produced from the engines. The EECs measure a lot of data to allow the engines to work as efficiently as possible, so there is a lot of data on engines parameters and thrust produced in different conditions.
The assumed temp method is basically just using that data for how much thrust is produced in different temperature conditions. As pilots we have RTOW tables which provide us with information for specific runways and how much weight we can lift with different winds and temperatures. The first thing we do is decide which engine rating we will use, this is dependant on runway length, conditions (wet etc) wind etc. The 3 settings we have for the 737-800 are 26k, 24k and 22k. The NG is very overpowered so we nearly always use 22k. We have our TOW and we use the tables to see what is the maximum temperature in which we could lift our specific take off weight.
An example: Say temp is 10deg and runway is 2800m with no wind. In these conditions say we can lift 75tons. However we only weight 65tons, so we can reduce the thrust by pretending that its hotter then it is. So we go up the table to find the temperature where we find the MTOW being 65 tons, say this is 40deg.
Does that answer the question? Not sure it does....let me know and try and word your question a little different and I'll see what I can do haha.
That's probably the simplest explanation I've seen/heard anyone give of what assumed temp t/o is
What I want to know is what parameters and calculations the FMC works with/within to come up with the %N1 when you enter an assumed temperature.
Only reason I ask is only for flight sim use - of course I don't have any RTOW tables (not for the NG anyway) and it'd be easier to work out if I could kinda reverse the calculation if that makes sense.
Given you usually use TO-2 derate - does that usually mean CLB-2 derate too?
Well as I understand the system, the FMC doesn't actually do the calculation. Remember all the systems are interlinked. It is the EECs that do all that kind of magic. So when you set an assumed temperature in the FMC, the FMC will then send this temperature to the EEC and the EEC will then return an N1 value. Same with using 22k etc, the FMC will send the signal to the EEC which will then limit itself to 22k. As for the actual maths that the EEC does well I don't think they will be simple for you haha, like I said it takes in a large amount of data and does its calculations to get the engines running how they should.
Yes if you use a derate for TO then you will have a CLB derate too, which will slowly increase to max as you climb.
Yes if you use a derate for TO then you will have a CLB derate too, which will slowly increase to max as you climb.
Yeah the more I read about what goes on between the FMC, EEC and the engines regarding assumed temp. the more I just want to forget about trying to work it all out
The only semi-useful thing I've read is regarding the P&W 744 engines and converting OAT to kelvin, and doing some more trickery pokery maths and it seems to come somewhere close. It doesn't seem to work for the 738 though. I have the RTOW tables I need for the 747 and of course it's a completely different kettle of fish from the NG.
I suppose most 738 operations will use a derate anyway as runway length isn't as much a factor as 744 operations can be so I'll leave the assumed temp as it is.
Soldato
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Here's one for you, Blinkz, sometimes on taxi when the plane does (what i would call) a rolling start, where the pilot doesn't stop to increase thrust on the runway but keeps going and increases thrust w/out stopping, it's happened when I've been on a plane a few times (in fact I don't think they've stopped before the turn off on the runway), what's the deal with that ?
This happened to me once before. My understanding was that the captain just got the all clear for takeoff and didn't need to stop before increasing the thrust. Obviously this is coming from someone who isn't a pro. Im sure Blinkz will have a better definition
Yea its called a rolling start, and its basically what Nymins says. We will get cleared to takeoff before or as entering the runway and so there is no need to stop the aircraft, stopping the aircraft just wastes runway for takeoff so there is no need for it. As we're turning onto the runway we will complete the final items of the before takeoff checklist and then thrust up the engines to around 40%, again this will probably still whilst the aircraft is turning onto the centreline, once the engines are stabilised and we are aligned with the runway we will set takeoff thrust and start the takeoff roll. Its not a big event, and its not that uncommon either. It all depends on the airport and how busy it is. If its a quiet airport then it is more likely to happen then at a busy one.
That's strange, the most times I've seen rolling starts is at Manchester between 1200 and 1500 when there's only 23R in operation for departure and arrivals - usually when things get really busy.
I always thought the aircraft taxiing or holding short would be told to make a rolling start because it would get them out of the way of the aircraft on final approach quicker than lining up and waiting.
I always thought the aircraft taxiing or holding short would be told to make a rolling start because it would get them out of the way of the aircraft on final approach quicker than lining up and waiting.
It all depends, there is minimum separations between aircraft taking off, so if one has just taken off then you won't be able to doing a rolling. But as you say if there is on on final then u need to go pretty sharpish! It all depends on the airport like I say.
No it doesn't! I've another question:
What is that sensation of turbulence it seems you get on take off sometimes? I would describe it as this: As soon as you are airborne, you experience lots of vibration, it almost feels like you are skidding on water, I find it makes me feel quite unsettled, I can't read a book while it is ahppenign as it makes me feel ill and once when it happened in Turkey last year I was worried we were crashing, because it was completely dark outside and no lights I could not tell our altitude. it was made worse by the fact that it felt like the plane was losing altitude - it was really disorientating. You know usually you can feel it moving upward? Well, this time it seemed like it was struggling - what kind of turbulence is that?
And don't answer, 'the kind that only exist in scared passenger's heads' - which is probably is!
Also had another one once in Madrid where at that exact really cool moment of weightlessness on takeoff, it felt like we were chucked back down again,9although we didnt hit the floror!) and then we started to climb, is that a windshear?
What is that sensation of turbulence it seems you get on take off sometimes? I would describe it as this: As soon as you are airborne, you experience lots of vibration, it almost feels like you are skidding on water, I find it makes me feel quite unsettled, I can't read a book while it is ahppenign as it makes me feel ill and once when it happened in Turkey last year I was worried we were crashing, because it was completely dark outside and no lights I could not tell our altitude. it was made worse by the fact that it felt like the plane was losing altitude - it was really disorientating. You know usually you can feel it moving upward? Well, this time it seemed like it was struggling - what kind of turbulence is that?
And don't answer, 'the kind that only exist in scared passenger's heads' - which is probably is!
Also had another one once in Madrid where at that exact really cool moment of weightlessness on takeoff, it felt like we were chucked back down again,9although we didnt hit the floror!) and then we started to climb, is that a windshear?
You sure its not just the G-Force of the aircraft taking off? I get the feeling of being pushed down into my seat sometimes because of the speed and rate that it is going up.
Edit: Also a Q for Blinkz. Where did you train? I thinking of going to PTC in Waterford, but not sure on what other places are like. Probably asked you this before, but i forget
Edit: Also a Q for Blinkz. Where did you train? I thinking of going to PTC in Waterford, but not sure on what other places are like. Probably asked you this before, but i forget
Edit: Also a Q for Blinkz. Where did you train? I thinking of going to PTC in Waterford, but not sure on what other places are like. Probably asked you this before, but i forget
OAA iirc?
No it doesn't! I've another question:
What is that sensation of turbulence it seems you get on take off sometimes? I would describe it as this: As soon as you are airborne, you experience lots of vibration, it almost feels like you are skidding on water, I find it makes me feel quite unsettled, I can't read a book while it is ahppenign as it makes me feel ill and once when it happened in Turkey last year I was worried we were crashing, because it was completely dark outside and no lights I could not tell our altitude. it was made worse by the fact that it felt like the plane was losing altitude - it was really disorientating. You know usually you can feel it moving upward? Well, this time it seemed like it was struggling - what kind of turbulence is that?
And don't answer, 'the kind that only exist in scared passenger's heads' - which is probably is!
Also had another one once in Madrid where at that exact really cool moment of weightlessness on takeoff, it felt like we were chucked back down again,9although we didnt hit the floror!) and then we started to climb, is that a windshear?
What is that sensation of turbulence it seems you get on take off sometimes? I would describe it as this: As soon as you are airborne, you experience lots of vibration, it almost feels like you are skidding on water, I find it makes me feel quite unsettled, I can't read a book while it is ahppenign as it makes me feel ill and once when it happened in Turkey last year I was worried we were crashing, because it was completely dark outside and no lights I could not tell our altitude. it was made worse by the fact that it felt like the plane was losing altitude - it was really disorientating. You know usually you can feel it moving upward? Well, this time it seemed like it was struggling - what kind of turbulence is that?
And don't answer, 'the kind that only exist in scared passenger's heads' - which is probably is!
Also had another one once in Madrid where at that exact really cool moment of weightlessness on takeoff, it felt like we were chucked back down again,9although we didnt hit the floror!) and then we started to climb, is that a windshear?
It would be great to get into it, but the cost would be a good bit more than PTC. Also its only down near Dublin, so it isn't too far away. Not keen on moving miles and miles away for it. I think PTC may be the only place in Ireland to do it? Could be wrong, hopefully there will be more in a few years.