A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2017 Dec 25, 03:13 -0800
RE : Shrier-dec-2017-g41010 and DavidPike-dec-2017-g41016 ... and also : RE : Couëtte-dec-2017-g40976
On Christmas Day, 2017
Dear Tracy and David,
David, thanks for "publishing" your Acceleration Corrections Table. It is great to "rediscover" it again after having set it aside for so many decades.
As you know, and except when in "heading" mode, Airliners fly alongside Great Circles from coordinates to coordinates and thus automatically correct for any lateral perturbation. Under such conditions there is no "systematic lateral" deviation of the vertical, even when encountering strong jet [clear sky] turbulence. These were most probably your prevailing environmental flight conditions, Tracy. Right ?
Therefore there would be no use in this case for the "lateral" / "constant heading" part of the Correction Table. Agree ?
The only possible systematic deviation to vertical would then have remained the longitudinal one in the case the Aircraft Ground speed were not constant.
Aircraft Ground speed is the vector sum of :
- TAS (true airspeed) which is approximately twice the IAS (indicated airspeed) at FL 360, and :
- Wind component along ground track.
Generally at such altitudes Airliners autothrottles maintain a constant Indicated Mach Number (IMN). Most often this yields a constant ground speed (+/- 1 knot over 1 minute of time) over a few elapsed minutes. However at constant IMN appreciable ground speed changes can and will occur - sometimes exceeding 10 kts/minute - mainly as a result of wind shift or static air temperature change.
Assuming that your aircraft was flying Great Circle, and in order to perform adequate longitudinal acceleration error corrections, Tracy you needed to access real time ground speed either from the cockpit - which I strongly suspect since you published both TAS and Wind and if so, hello Dear Colleague ! - or from some gps portable device, from which you had to transform such ground speed changes into the appropriate units (generally knots/minute) in order to derive your own longitudinal acceleration correction e.g. from some Correction Table such as yours, David. Right also ?
Yes ! I would certainly be interested to know, Tracy, which instrument you were using and from which area in your Aircraft.
Meanwhile, - RE : Couëtte-dec-2017-g40976 - Jupiter was still quite close from Zubenel Genubi when flying from Fort de France Martinique French West Indies to Paris Orly 2 nights ago. And as being almost abeam the starboard side of the Aircraft when arising from the horizon, both were immediately visible from both seats in the cockpit. Both subsequently kept showing almost exactly at the same height for one hour or so until they vanished in the dawn light, shortly after flying abeam the Azores Islands for us our starboard side.
I flew A343 "9H-SUN" between FDF and ORY yesterday very early morning, but ... my favorite A340 has remained flying the magnificent A345 "CS-TFX".
Only one week left of Long Haul Flying since after my 15 day vacation, I will have to retire after having reached the age of 65 ... Trying to smile through my tears though, as I will keep on flying as a volunteer no salary Instructor in an Airclub, until I can reach Heaven for ever as keep hoping.
Meanwhile, Merry Christmas to you all.
Antoine M. "Kermit" Couëtte