Two quick questions about two flights
Thread Starter
Two quick questions about two flights
A couple of things on two recent flights occurred that I've never experienced before, and hoped someone might be kind enough to offer an explanation. This is simply to satisfy my curiosity.
1) Flying LAX to DFW on Monday, about 45 minutes from landing the aircraft suddenly slowed by about 20 knots. I thought we were actually starting an early descent, but checked the flight map on the IFE and saw we had slowed but not descending. About a minute or two later we sped up again. What might be the reason for this - sequencing?
2) Next day flew DFW to HNL. About two hours out we climbed to 39,500 feet (confirmed by the flight map and FlightAware). I can't recall ever being on a flight that flew with that increment of 500 feet above a "normal" flight level. What might be the reason for this?
My thanks in advance.
1) Flying LAX to DFW on Monday, about 45 minutes from landing the aircraft suddenly slowed by about 20 knots. I thought we were actually starting an early descent, but checked the flight map on the IFE and saw we had slowed but not descending. About a minute or two later we sped up again. What might be the reason for this - sequencing?
2) Next day flew DFW to HNL. About two hours out we climbed to 39,500 feet (confirmed by the flight map and FlightAware). I can't recall ever being on a flight that flew with that increment of 500 feet above a "normal" flight level. What might be the reason for this?
My thanks in advance.
Thread Starter
This one actually showed airspeed (as well as ground speed and "true air speed"), but the big clue we had slowed was the reduced noise from the engines and the sudden feeling of deacceleration followed a couple of minutes later by the reverse happening. I don't think it was wind.
ETA: I hope this link works:
https://flightaware.com/live/flight/.../KDFW/tracklog
At 10:31:25 pm EST you can see the speed drop and then recover shortly afterwards.
ETA: I hope this link works:
https://flightaware.com/live/flight/.../KDFW/tracklog
At 10:31:25 pm EST you can see the speed drop and then recover shortly afterwards.
Your body has no way of telling whether or not that's due to an increased headwind component.
Thread Starter
Then why did the engines sound like they had gone to idle? PS. I should also add that the map on the AA 321s also gives you the head or tail wind - that did not change.
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The only folks who knew are the folks at the front end. I suspect that you will never know what they were testing and verifying at that point. Happily, all ended the way it was planned.
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First I will start with a rhetorical question -
If you were puzzled, why didn’t you ask on disembarkation? Most pilots are a friendly bunch, and are quite happy to have a quick visit to the Flight Deck.
Onto your questions - (and any answers you get here will be pure speculation)
1 - possibly streaming, then decided against it. I have had numerous occasions where ATC have asked me to either speed up or slow down, then shortly after they have changed their minds and we have gone back to “normal” speed.
2 - was the Flight oceanic by this stage? If so, are there US offset procedures that includes flying at an out of the ordinary level? I’m clutching at straws........
If you were puzzled, why didn’t you ask on disembarkation? Most pilots are a friendly bunch, and are quite happy to have a quick visit to the Flight Deck.
Onto your questions - (and any answers you get here will be pure speculation)
1 - possibly streaming, then decided against it. I have had numerous occasions where ATC have asked me to either speed up or slow down, then shortly after they have changed their minds and we have gone back to “normal” speed.
2 - was the Flight oceanic by this stage? If so, are there US offset procedures that includes flying at an out of the ordinary level? I’m clutching at straws........
Possible block altitude request....I have done it many times with obvious approval from ATC...slowed down prior to TOD? Happens all the time.....been slowed 3 hrs away from JFK🙄
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The mind and body can play tricks. The deceleration to felt could well have been accurate - most likely at ATC request for en-route seperation or arrivals sequencing. Passenger aircraft are designed to be as efficient as possible, and that means minimising drag. In addition, the amount of kinetic energy involved in >50T of metal, fuel and flesh travelling at 500kts is significant.
What this means is that a deceleration of 20kts IAS or more could take a minute, or longer. During that period, one's body can adjust and perceive the deceleration as the new norm. When the target speed is achieved, more power will be required to maintain it (although typically not as much as the previous cruising speed), so the engines will spool up as required. This can feel like an acceleration - partly because one's body had created the new normal of a roughly constant deceleration rate, and because our minds associate an increase in thrust with acceleration. Furthermore, the new speed will require a higher pitch attitude than before, with more of one's weight acting through the back of the seat, rather than the bottom. It's a small change, but it serves to strengthen the illusion.
The most extreme examples of this are a descent with flap out at constant speed to level flight. If the level off coincides with a turn - and thus increased lift required, induced drag and,as such, power required; the resulting pitch change and increase in thrust can feel very much like the chaps/chapesses at the front have decided to "step on it".
What this means is that a deceleration of 20kts IAS or more could take a minute, or longer. During that period, one's body can adjust and perceive the deceleration as the new norm. When the target speed is achieved, more power will be required to maintain it (although typically not as much as the previous cruising speed), so the engines will spool up as required. This can feel like an acceleration - partly because one's body had created the new normal of a roughly constant deceleration rate, and because our minds associate an increase in thrust with acceleration. Furthermore, the new speed will require a higher pitch attitude than before, with more of one's weight acting through the back of the seat, rather than the bottom. It's a small change, but it serves to strengthen the illusion.
The most extreme examples of this are a descent with flap out at constant speed to level flight. If the level off coincides with a turn - and thus increased lift required, induced drag and,as such, power required; the resulting pitch change and increase in thrust can feel very much like the chaps/chapesses at the front have decided to "step on it".
Thread Starter
Thanks, everyone, appreciate your answers. Smokey - I think you have the answer that satisfies me the most for the deacceleration - we were close to DFW so would not be surprised if we were slowed for separation. As for the altitude question - atr-driver, I assume a "block altitude request" means you can request a "block" of altitude space and then fly at any altitude within that block. Is that correct?
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Excuse my late arrival, the engines went to flight idle halfway across the Indian Ocean, well at least midway between Sumatra and Mauritius.
I have noticed this phenomenon on many round trips Kuala Lumpur to Johannesburg, more than 100 round trips, and agree it is in order achieve a spot on arrival time at destination.
It can be disconcerting when 3 hours from the nearest land mass.
I have noticed this phenomenon on many round trips Kuala Lumpur to Johannesburg, more than 100 round trips, and agree it is in order achieve a spot on arrival time at destination.
It can be disconcerting when 3 hours from the nearest land mass.
Excuse my late arrival, the engines went to flight idle halfway across the Indian Ocean, well at least midway between Sumatra and Mauritius.
I have noticed this phenomenon on many round trips Kuala Lumpur to Johannesburg, more than 100 round trips, and agree it is in order achieve a spot on arrival time at destination.
It can be disconcerting when 3 hours from the nearest land mass.
I have noticed this phenomenon on many round trips Kuala Lumpur to Johannesburg, more than 100 round trips, and agree it is in order achieve a spot on arrival time at destination.
It can be disconcerting when 3 hours from the nearest land mass.
Still, it could have been worse - if they had stopped completely, you could have been up there all day ...
Thread Starter
PS. This has been bothering me for a day or two:
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
No, that is absurd. Anyone on an aircraft will feel a change in velocity in their reference frame, i.e., that of the aircraft, not the ground.
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
No, that is absurd. Anyone on an aircraft will feel a change in velocity in their reference frame, i.e., that of the aircraft, not the ground.
PS. This has been bothering me for a day or two:
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
No, that is absurd. Anyone on an aircraft will feel a change in velocity in their reference frame, i.e., that of the aircraft, not the ground.
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
No, that is absurd. Anyone on an aircraft will feel a change in velocity in their reference frame, i.e., that of the aircraft, not the ground.
Thread Starter
Dave - I've been on flights where the ground speed varied from 450 to 650 knots. There was no feeling of acceleration on any of those flights other than take off, ascent, descent and landing. I suspect you have your physics wrong if you think anyone on an aircraft will feel a change in velocity because it changed wrt to the ground during the cruise. The frame of reference is the aircraft, not some point on the ground.
I do have a little bit of background in physics if you had taken the time to do a little research. It's a shame; I've asked for help on this site and also offered my advice on this site, but to come across someone who 1) didn't read my posts carefully and 2) doesn't understand Newtonion physics but insults me anyway, well, that's your choice.
For your info, I have used Newton's laws to find, track and take spectrosopic data of space debris among other things. I think you should sit back and reconsider your posts.
I do have a little bit of background in physics if you had taken the time to do a little research. It's a shame; I've asked for help on this site and also offered my advice on this site, but to come across someone who 1) didn't read my posts carefully and 2) doesn't understand Newtonion physics but insults me anyway, well, that's your choice.
For your info, I have used Newton's laws to find, track and take spectrosopic data of space debris among other things. I think you should sit back and reconsider your posts.
Dave - I've been on flights where the ground speed varied from 450 to 650 knots. There was no feeling of acceleration on any of those flights other than take off, ascent, descent and landing. I suspect you have your physics wrong if you think anyone on an aircraft will feel a change in velocity because it changed wrt to the ground during the cruise. The frame of reference is the aircraft, not some point on the ground.
I do have a little bit of background in physics if you had taken the time to do a little research. It's a shame; I've asked for help on this site and also offered my advice on this site, but to come across someone who 1) didn't read my posts carefully and 2) doesn't understand Newtonion physics but insults me anyway, well, that's your choice.
I do have a little bit of background in physics if you had taken the time to do a little research. It's a shame; I've asked for help on this site and also offered my advice on this site, but to come across someone who 1) didn't read my posts carefully and 2) doesn't understand Newtonion physics but insults me anyway, well, that's your choice.
1) I have read your posts carefully
2) I did not insult you, I simply pointed out that your denial ("that is absurd") of my statement that
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
In fact you appear to have conceded that you will feel those forces on takeoff and landing, where again it is the change in speed of the aircraft over the ground that produces the sensation you feel. The only difference between that and acceleration/deceleration in the cruise is one of degree - the physics is exactly the same, only the numbers differ.
You go on to misquote me
"you have your physics wrong if you think anyone on an aircraft will feel a change in velocity because it changed wrt to the ground during the cruise"
I'll give you the benefit of the doubt and assume that wasn't an intentional straw man argument, but I stand by my comments.
Thread Starter
I stand by my comments, Dave, you have your physics wrong.
"when I actually said that IF you feel a sensation THEN it's because the aircraft's speed is changing, not the other way round (I grant you that the sensation may be imperceptible)."
You wrote:
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
I'm not pursuing this further, it seems pointless. You've now agreed with my point that it's the speed of the aircraft that's changed, therefore those in that reference frame will feel the change in speed, but then back up your point with the argument that it's ground speed. Sorry, no more time for this nonsenseother than to say:
Thanks to those that gave helpful answers.
"when I actually said that IF you feel a sensation THEN it's because the aircraft's speed is changing, not the other way round (I grant you that the sensation may be imperceptible)."
You wrote:
"If you felt a deceleration (i.e. the effect of inertia), all that tells you is that your speed over the ground was reducing."
I'm not pursuing this further, it seems pointless. You've now agreed with my point that it's the speed of the aircraft that's changed, therefore those in that reference frame will feel the change in speed, but then back up your point with the argument that it's ground speed. Sorry, no more time for this nonsenseother than to say:
Thanks to those that gave helpful answers.
We're agreed on that.
I have never disputed that.
It's self-evident, thanks to Newton, that the only speed change a body can detect is acceleration in free space, which in the case of an aircraft implies a change in groundspeed. We learned that in 1728.
You've now agreed with my point that it's the speed of the aircraft that's changed, therefore those in that reference frame will feel the change in speed, but then back up your point with the argument that it's ground speed.
It's self-evident, thanks to Newton, that the only speed change a body can detect is acceleration in free space, which in the case of an aircraft implies a change in groundspeed. We learned that in 1728.