Calculating groundspeed from DME?
Calculating groundspeed from DME?
Joined: Jul 2005
Posts: 3
Likes: 0
From: Nottingham, UK
From the DME, note the distance travelled in 36 seconds. Since 36 seconds = 1% of one hour, multiply this figure by 100 to get the groundspeed.
I seem to remember that this is particularly well-suited to fairly fast a/c (i.e. > 250 kts), presumably because the absolute error in speed is less significant, as is the absolute error caused by the difference in slant range -vs- track miles.
I seem to remember that this is particularly well-suited to fairly fast a/c (i.e. > 250 kts), presumably because the absolute error in speed is less significant, as is the absolute error caused by the difference in slant range -vs- track miles.
Joined: Jun 2001
Posts: 3,991
Likes: 8
From: UK
Well I wished I had been given a penny for every groundspeed check I did using DME when I was on the B737-200!!
For a quick check 36 secs is OK but I used to used 3 or even 6 mins if I wanted a really accurate one.
Mind you, after a while you got that good at it that you could watch the DME (barrel type presentation) rate of change and take a good guess at the groundspeed.
It was quite amusing after a long day to be airtaxied back home and they had groundspeed and time to station read out - such luxuries!!
For a quick check 36 secs is OK but I used to used 3 or even 6 mins if I wanted a really accurate one.
Mind you, after a while you got that good at it that you could watch the DME (barrel type presentation) rate of change and take a good guess at the groundspeed.
It was quite amusing after a long day to be airtaxied back home and they had groundspeed and time to station read out - such luxuries!!
Joined: Sep 2001
Posts: 339
Likes: 0
From: Eagan, MN
Well, there could be so many derived formulas....the ones previously mentioned, radial to arc, arc to radial, it became second nature. All now lost, as in elementary school my grandson now uses a calculator for what had to become 2nd nature for us...the times tables,etc. Progress? We old fogies know it could be done, and could be 2nd nature. We marvelled at guys being able to do Adcock Range approaches, and even more 'basic' approaches, before 'our time'.. That we didn't have to do them with oh so modern ADF-DME-VOR-Loran-Starshots, just means time marched on, I guess. And it continues, and nothing really changes.
