478 vs 588 kts...

[Robini]

God Evening My Gentlemens,
I was flying (A330....again....) the last year and on the monitors it
first said info: s in Metres and KM/H and later Feet and MPH...
BUt the funny thing is that it said we were flying at 1089 km/h wich
is about 588 knt. And when you got the MPH info it said 550 MPH and that¨s
about 888 km/h=478 knt...So is the GS 478 knt and the TAS 588 knt?
So we were flying at 478 knt but we had a headwind at 110 knots?
I'm not getting surpriced if it was that kind of strong winds, cause the flight
landed many minutes late....
Thanks!

[sapperkenno]

How long was it between you checking the two values?

It wouldn't be impossible to pick up that kind of headwind in a relatively short period of time.

The only other thing you need to know is what exactly the display shows, which is somewhere else on here. Just do a search.

I read something similar a while ago, and believe the pax screens show GS (in values the public are familiar with; MPH/KPH) which is taken from the Air Data Computer(s). On BA747's I've travelled on, it also tells you the head/tail wind component, which I found interesting.

Maybe it's simply because Boeing make better airplanes... Or shall we not go down that route... ;)

Hope that helps.

[Robini]

Hello Sapperkenno,
I checked them at the same time. We didn't have the same speed all the time,
but it said 1000-1100 km/h under the whole flight. But at the same time it also
said around 550MPH so i'm getting a bit confused here ;)
The route was GOT-SHJ wich is about 4947 km and if we would have this
kind of speed we would reach Sharjah in a very short time.
The funniest thing is that we landed late when we departed in time (for once).

Little deeper look in this searching get's following:
We got to FL280 after 330 km climbing, we waited for some reason
(maybe x-tremly heavy cause it was night and no traffic above).
We continued to climb after some minutes waiting, to FL370.
From FL280 to FL370 it took 250 km. So total distance to getting to
altitude cruising was about 580 km.
BTW when we got lighter later in the flight we went to FL390...

Not exactly sure when we began our decend but say typical 300 km before
reaching destination.

580+300= 880 km was during no cruise...

4947-880=4060 km in cruise

During cruise it took about 5 h 30 min...

4060/5,5= 738 km/h wich is about 400 knt...

Logically we couldn't even have reached 588 kt?
Cause we seemed to have quite strong headwinds....

[ATCast]

Hello Robini,

It is not uncommon for the entertainment system to be incorrect. I recently travelled on an A340 where I noted a similar error. It turned out that for a certain unit (can't remember whether it was kph, kts or mph) it added the headwind to the airspeed to obtain groundspeed.
When I selected the other units, the headwind was correctly subtracted from the airspeed to obtain groundspeed.

Rgrds,

ATCast

[Old Smokey]

Did your route involve a large Track change? Only yesterday I was enjoying a nice 115 Kt Tailwind, executed a 70 degree Track change (in one of those areas where there's some nasty stuff going on), and the wonderful Tailwind bacame almost all Crosswind. Relatively constant TAS and Wind, Large Track change dramatically affecting Wind Component and Ground Speed.

Just Wondering.......................:confused:

Regards,

Old Smokey

[Robini]

I was quite tired when answered.... Our flight from Gothenburg to Sharjah UAE
was a bit longer anyway. We aren't allowed to pass the airspace of Iran so we
flew moore like this : GOT-IST-SHJ wich is about 5200 km, so the flight was
slightly longer than i said above....

But anyway it sounds like quite fast, cause we didn't slow down so much during
the flight...

//R