BAW = Callsign Speedbird - Literally.
Aug 21, 2017, 10:02 am
#31
Join Date: Jan 2016
Location: LHR/ATH
Programs: Amex Platinum, LH SEN (Gold), BA Bronze
Posts: 4,489
In one sense you are correct... ground speed does not indicate how fast the aircraft is travelling through the air.
On the other hand, you use the term "indicated airspeed" which is not correct either. As an aircraft climbs into thinner air the air has less effect on the airspeed indicator and so it under-reads... by quite a lot! So the indicated airspeed also won't show the real airspeed either and an adjustment has to be made to allow for the reduced density.
For example... an airliner doing a true airspeed of 500Kts at 38,000ft will likely have an indicated airspeed of around 280Kts!
The Mach meter on the other hand will show the percentage of the speed of sound in the conditions in which the aircraft is flying... the speed of sound depends on the density (and hence temperature) of the air so at sea-level it is about 660Kts and at 35,000 (-55C) it is about 575Kts
Sorry to get technical but it is an interesting topic of Indicated, vs True airspeed vs ground speed vs Mach number.
On the other hand, you use the term "indicated airspeed" which is not correct either. As an aircraft climbs into thinner air the air has less effect on the airspeed indicator and so it under-reads... by quite a lot! So the indicated airspeed also won't show the real airspeed either and an adjustment has to be made to allow for the reduced density.
For example... an airliner doing a true airspeed of 500Kts at 38,000ft will likely have an indicated airspeed of around 280Kts!
The Mach meter on the other hand will show the percentage of the speed of sound in the conditions in which the aircraft is flying... the speed of sound depends on the density (and hence temperature) of the air so at sea-level it is about 660Kts and at 35,000 (-55C) it is about 575Kts
Sorry to get technical but it is an interesting topic of Indicated, vs True airspeed vs ground speed vs Mach number.
Aug 21, 2017, 10:06 am
#32
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Join Date: May 2011
Location: London
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I can't remember all the detail but this time last year on the end of a hurricane we did Halifax (YHZ) - LHR, 2857 miles in spot on four hours - 715 miles an hour on average on an Air Canada 767. Some of it must have been a whole lot faster!
Aug 21, 2017, 10:11 am
#33
Join Date: Mar 2011
Location: Tyrone,EU
Programs: Avios Hunter
Posts: 2,812
no no, it doesn't work like that. Indicated speed and ground speed are completely different. 745 MPH Ground speed with a 100 MPH tailwind is still 645 MPH indicated speed, so the air indicator would still show like Mach 0.85 or so in the cockpit, nothing near 0.99 MACH indicated! Anything above 0.86 or so MACH in a 777 and you would be getting overspeed warnings which really isn't a good thing, the plane would have to be checked over and the pilots in big trouble.
So it is physically impossible for any commercial jet in the air right now to come anywhere near the speed of sound in level flight no matter how strong the tail wind is, they would have to do a crazy dive.
So it is physically impossible for any commercial jet in the air right now to come anywhere near the speed of sound in level flight no matter how strong the tail wind is, they would have to do a crazy dive.
Aug 21, 2017, 10:27 am
#34
Join Date: Feb 2009
Location: YYC
Programs: BA bronze, Aeroplan peon
Posts: 4,747
Well, if a plane is travelling over the ground at 745 MPH, it is travelling at 745MPH, which 22 MPH short of SOS, which is pretty close in my book. The fact that 100MPH of that is coming from a tail wind and thus the indicator is showing substantially less, doesn't affect how quickly it is going from A to B.
Aug 21, 2017, 10:29 am
#36
Join Date: Jun 2016
Location: Cumbria, UK
Programs: BAEC - Silver
Posts: 107
Well, if a plane is travelling over the ground at 745 MPH, it is travelling at 745MPH, which 22 MPH short of SOS, which is pretty close in my book. The fact that 100MPH of that is coming from a tail wind and thus the indicator is showing substantially less, doesn't affect how quickly it is going from A to B.
As it happens most commercial transport aircraft do fly well into the transonic region above Mcrit, so while they stay (quite a way) below Mfreestream 1.0, some of the local flow will be supersonic and there will be normal shockwaves forming at various points round the fuselage. For longer haul aircraft the greater amount of sweepback and the supercritical wing allow Mcrit to get closer to Mfreestream 1.0 so something like the A380 has a Mcrit of i think 0.84, and an Mmo of 0.89 so can (and will) fly well into the transonic region and gets closer to Mfs 1.0 than for example the A320 with a smaller sweep angle.
Aug 21, 2017, 10:41 am
#37
Join Date: Apr 2003
Location: Seattle, Wash. USA
Posts: 1,531
I recall being held at LAX for an hour at the start of a LAX-SYD flight, due to unusually light headwinds that would have caused us to break the curfew at SYD. Not a fun start to a 14+ hour flight. Coming back a couple of weeks later, we had a great tailwind and made the crossing in 12 hours. On that route, ATC have something called Flextrack that allows the pilots some latitude (literally!) to sniff around for the best winds en route and change course accordingly.
Aug 21, 2017, 12:32 pm
#38
Join Date: May 2014
Location: DMV
Posts: 2,092
While I've seen this happen a lot on eastbound transatlantic flights due to the prevailing westerlies over the North Atlantic and the jet stream, I've only seen it once on a westbound transatlantic flight Dublin to New York. The plane left 45 minutes late and arrived an hour early. My only explanation is that it must have ridden the anticyclonic winds on the backside of a low pressure system over the Atlantic.
Aug 21, 2017, 12:53 pm
#39
Join Date: Mar 2016
Location: Plymouth, UK
Programs: BAEC Gold
Posts: 1,159
As an ex commercial pilot myself I miss all that techy stuff!
Aug 21, 2017, 12:58 pm
#40
Join Date: Aug 2011
Location: Kentucky/Japan
Programs: UAL 1k
Posts: 57
The fastest I have seen was while flying a Citation X. Normal cruise for us was .92 Mach which was also the MMO. We had a tailwind in excess of 200 headed east over central Canada and saw a groundspeed of right around 800mph.
Aug 21, 2017, 1:12 pm
#41
Original Poster
Join Date: Apr 2014
Location: Paynesville, Vic
Programs: BA Gold AVIS Presidents Club
Posts: 356
Thanks all for posting... I was genuinely interested on other FTs experiences where quick flight times were involved.
I may be offline for a while as apparently I need to go back to school to brush up on my grammer or was that grammar ?
In the meantime I shall review the meaning / application of 'literally' as homework.
OF
I may be offline for a while as apparently I need to go back to school to brush up on my grammer or was that grammar ?
In the meantime I shall review the meaning / application of 'literally' as homework.
OF
Aug 22, 2017, 8:49 am
#42
Join Date: Mar 2011
Location: Tyrone,EU
Programs: Avios Hunter
Posts: 2,812
What that got to do with measuring the speed of a plane ?
The speed of sound is 767 MPH.
The speed of the plane was 745 MPH.
The plane is travelling 22 MPH slower than the speed of sound in still air.
Now if you want to start talking about the speed of sound in or around the plane, that's another matter.
There's a difference between something "breaking the sound barrier" and something travelling at a comparable speed that sound travels at.
A bullet fired from a moving gun might be travelling faster than the speed of sound, but it might not "break the sound barrier" depending on how fast the gun is moving and how fast the bullet came out of it.
The speed of sound is 767 MPH.
The speed of the plane was 745 MPH.
The plane is travelling 22 MPH slower than the speed of sound in still air.
Now if you want to start talking about the speed of sound in or around the plane, that's another matter.
There's a difference between something "breaking the sound barrier" and something travelling at a comparable speed that sound travels at.
A bullet fired from a moving gun might be travelling faster than the speed of sound, but it might not "break the sound barrier" depending on how fast the gun is moving and how fast the bullet came out of it.
Last edited by tangey; Aug 22, 2017 at 8:57 am
Aug 22, 2017, 9:11 am
#43
Join Date: Mar 2016
Location: Plymouth, UK
Programs: BAEC Gold
Posts: 1,159
True... except that when people generally talk of travelling faster than the speed of sound they generally mean breaking the sound barrier... though I accept they are very different things.
Aug 22, 2017, 10:01 am
#44
Moderator: British Airways Executive Club
Join Date: Jan 2009
Programs: Battleaxe Alliance
Posts: 22,127
I have trouble seeing what is particularly unfriendly about Sydney
There are quite a few countries that can use the self service immigration whereas in UK , smeone arriving on an AU passport would have to queue under any passports and not have to queue
With departures, just about all can use self service immigration desks
Domestic departures have very short queues for security (ime) and there is no issue with liquids
What is unfriendly about it?
The curfew is a good thing given how close the airport is to residential properties
There are quite a few countries that can use the self service immigration whereas in UK , smeone arriving on an AU passport would have to queue under any passports and not have to queue
With departures, just about all can use self service immigration desks
Domestic departures have very short queues for security (ime) and there is no issue with liquids
What is unfriendly about it?
The curfew is a good thing given how close the airport is to residential properties
Immigration arrangements are Australian government policy, not thanks to SYD
Forced walk through extensive duty free both on departure and arrival (much more than LHR T5)
Lack of domestic liquid restriction is not thanks to SYD, it's the Australian government policy
50%+ of self-service immigration machines closed for departure most of the time
Extremely bad trolleys at SYD that are well past their replacement date according to trolley staff
Need I go on?
If we think T5 is bad, SYD is far, far worse. However, this is a bit OT so enough about SYD... except to say I so wish BA flew to MEL instead of SYD. Much better airport - by 10,000% or more.
