The transcripts end at 7:41 when 305 takes off. Unknown if Nicky’s audio files extend beyond that time.

These audio files might, repeat might, include the audio from the ARINC radio link.  This depends on how many frequencies ARINC had and where they were located.  In addition to the one at SEATAC there was apparently another ARINC site at Portland International Airport since the airliner reported its takeoff, ETA, and other information within minutes of the takeoff from Portland.

But the Seattle ATC Center audio would end as soon as the aircraft was a few miles south of SEATAC and the controllers switched to transmitting and receiving through remoted sites.

An interesting thing I noted about the radio transcripts is that they end at 7:41. However, there is no indication that 305 is airborne by this time. The FBI puts the time of take-off at 7:36.

Is there any explanation for this discrepancy?

The airliner was cleared for takeoff while on the SEATAC tower's ground control frequency.  The flight crew was told to bypass the tower's other functions and contact the Seattle ATC Center immediately after takeoff.  The flight crew gave the takeoff time as 7:36 PM and they were airborne and talking to a Seattle Center controller at 7:37:11 PM.  Note that the tower and center controllers are not colocated and have different functions.  The Seattle Center controllers are in Auburn I think.

Anyone with a VHF radio could listen in on the airliner/center communications for a few minutes until the airliner was some distance south of SEATAC.  I don't see anything here that is a problem.

R99,

Changing the subject a bit, in your experience, would you describe what happened to 305 as a "phugoid"?

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In looking into the terms "oscillations", "fluctuations" and "bump", I ran across it and thought it might describe what was happening to Scott and the crew. What do you think?

My short answer would be "no".  In the simplest terms, the Boeing 727 would have two longitudinal stability issues to consider in its design in order to be approved by the FAA.

First is "static stability" which essentially just means that the aircraft center of gravity must be forward of the aircraft center of lift.  When an aircraft is trimmed out in flight in smooth air and is disturbed from that stable condition by something, the static stability acts immediately to return the aircraft to its original state and is probably not going to be noticed by the pilot even if he is hand-flying the aircraft.

But there is a second solution to that stability equation and that is the phugoid and it will be noticed by the hand-flying pilot.  The pilot will be the one to counter the phugoid and get the aircraft back into a stable and trimmed condition.  It is my understanding that the phugoid was pretty bad at high altitudes on the original jet transport aircraft such as the 707.  The autopilot could compensate for the phugoid but if the autopilot was not functional then the pilots had to hand fly the aircraft and that could be very tiring over a period of several hours.

In the case of the hijacked airliner, if the "oscillations" actually referred to changes in aircraft pitch angles (as opposed to cabin pressure changes), my guess is that they would be caused by Cooper stepping on the steps below the hinged portion in order to create space for throwing out things that he did not want to take with him.  Lowering the hinged portion of the stairs would act as a downward movement on the aircraft elevators and result in pitch changes.  And if the aircraft was on autopilot, it would probably compensate for this and not be very noticeable to the crew if at all.     

Thanks, R99.

The problem I am running into is that "pressure oscillations" and "pressure fluctuations" are not commonly used aviation terms. Also, the description given by the crew of these terms don't seem to make sense. Were they only detected on the instruments? Or were they physically felt?

I imagine them being the same sensation as driving with only one back window down in your car.

I would not describe the terms you mention as "not commonly used aviation terms".  I think Anderson noted pressure fluctuations on the cabin altitude gage on the Flight Engineer's panel.

And I think the stairs slamming into the fuselage was sufficient to cause a physical reaction of the crew.  Rataczak reportedly said that it was sufficient to dislodge his radio headset.

Thanks, R99.

The problem I am running into is that "pressure oscillations" and "pressure fluctuations" are not commonly used aviation terms. Also, the description given by the crew of these terms don't seem to make sense. Were they only detected on the instruments? Or were they physically felt?

I imagine them being the same sensation as driving with only one back window down in your car.

While I can't quite find the reference at the moment, I believe it has been discussed on this forum that the crew reported feeling the nose of the plane dip slightly around the time of the pressure bump.  I suppose it's open to interpretation whether it was related to the bump or not. 

Sounds like Bill Rataczak talking.

...

interesting. where did those "unreleased" atc tapes come from?
I've not been following the thread.