In post # 50 above I mentioned the "black box" from which the flight path of Hotel Golf was reconstructed after the Stockport crash, and in post # 52 "forget" wrote that the Trident was the first commercial aircraft in which such a device was installed.
With respect, as we lawyers say, the Report I mention in the post immediately above narrates at Part IV that Hotel Golf was equipped with a Midas Type CMM Flight Recording system which recorded information simultaneously on two magnetic tapes, one housed in an armoured and fireproof container sited in the tail and designed to survive an accident, the other located on the cock pit floor. Both tapes were recovered. The tape from the protected recorder was undamaged. The other was "virtually undamaged" though the cassette was thrown from the electronics unit by the impact force.
The parameters recorded were indicated airspeed, pressure altitude and heading. Normal acceleration in each direction along the normal axis of the aircraft should also have been recorded, but was not for reasons that could not be determined.
The AIB working group was able to reconstruct what hapened during the last 900 seconds of flight. The rate of descent was a fairly steady 200 f.p.m. until at the very end there was a "sudden loss of height at the rate of 2000 f.p.m."
The Report includes, as I wrote before from memory, plots in azimuth and elevation, energy plot, and combined information plot.