The approach that I'd suggest is rubber banding the volumes on the audio tracks.
A 5.1 recording should result in 4 audio tracks on the timeline (channels 1/2 = L/R; channel 3 = C; channel 4 = LFE; channels 5/6 = rear FX). Hitting V on the keyboard results in a blue volume 'rubber band' appearing along the middle of the audio track. Each audio track needs to be separately highlighted and then V pressed. You can then adjust the volume of each track by using automation (which can be manually adjusted later), or you can adjust the volume wholly manually by double clicking on the blue line at the point where you want a change in volume to commence or end - double-clicking creates a node on the blue rubber band. The node can be moved up or down to increase or decrease the volume. To create a soundscape where the sound of the plane moves from front to back, progressively decrease the volume via the rubber band on audio tracks 1/2 and 3 while simultaneously progressively increasing the volume via the rubber band on audio channel 5/6. I suspect that the LFE would not need to be adjusted but, of course, it can be adjusted if it is needed.
Also, rubber banding is touched on a bit at about 55 minutes into SCS's webinar on Sound Forge/Spectral layers, and audio automation is also looked at extensively in another Webinar called Vegas Pro 11 Mixing Console. The Webinars are on SCS's website under 'Training', but selecting Training at the moment goes to a dead link.
Others on the forum may have other suggestions which would be great as I'd really like to know of other approaches to using 5.1 myself.
The problem with panning (any method) is that the tracks have already been recorded so you won't be panning just the jet, but everything on the tracks. It's going to sound a little weird when the front tracks go deathly silent as you reach the end of your pan.
I would probably try copy/pasting the tracks (so you now have a twin set of tracks). Leave the original tracks alone, Do a little eq-ing on the twin tracks to emphasize the jet and pan that. Then it's just a matter of playing with gains between the original tracks and the twin tracks until you get the effect you're looking for.
That is a good idea about duplicate tracks. Ive not had much time, but I tried quite an extreme test and the result wasn't that great, not much differentiation between front and back which was surprising as I had front and centre speakers up high with back right down low then switching the other way round.
Could be down to my amp setup as it is quite old. Investigation required.
I *THINK* the rear speakers are calculated on these surround sound cams and not actually recorded.
My old Sony SR11 (5.1 surround) cam up and died so just out of curiosity I pulled it apart to have a look at the mics. What I found were 3 of them... not enough to truly RECORD 5.1 surround... but enough to CALCULATE.
Now the calculating (if that is indeed what is happening) although pretty good in pristine situations... is not that great compared to an actual 5.1 recording.