View Full Version : How far away can you eyeball a CB
I'm aware of the theoretical line of site calc (from the ATPL VOR range question). How far though will the atmosphere let you see a significant Cb?
I was over Amsterdam at FL370 the other day and my colleague thinks LHR is clear of Cbs. I told him we would not see them from there but could not give him anything scientific.
reynoldsno1
13th Jun 2005, 22:07
FL360 at night south of Crete could see the b*st*rd over Malta - FL420 didn't hack it either, had to go round......
Maude Charlee
14th Jun 2005, 10:43
Line of sight calcs wouldn't give the best answer, as that is for distances between ground stations and a/c. I dare say the tops of a significant CB would be visible from FL390 or similar from a much greater distance in perfect atmospheric conditions, over twice the theoretical VHF distances (you need a mathematical whizz to work out the lenght of a tangential line from the a/c to the CB tops).
It was day and as we were 250 NMs away your answers confirm my thoughts - cheers.
MC - The LOS does take into account heights of a/c and cloud tops
1.25 X (SQ RT H1 + SQ RT H2)
In reynolds case 1.25 X (190 + 205) = 500 miles which roughly equates to Malta - Crete.
It seems that nominal atmospheric conditions roughly half the LOS calcs for a daytime Cb (no TS to help you spot them)
autoflight
15th Jun 2005, 01:13
In my experience, an isolated CB with top around FL 500 or greater, in clear daytime conditions, should be easily visible for more than 300 NM from jet cruising levels.
AF - The CBs in question were only FL250....you probably call them towering Cu in Oz.
My calcs say at FL500 theoretical LOS is 540..so with the divide by two theory 270NMs is not too far out from your 300.