The question was asked earlier in the thread , but
AFAIK was never answered...do 109s carry flight data recorders?
Thanks
No, there is no legal requirement. I'm not certain if one is available for the A109 Power, I think not.
The pilot would have had the London QNH set. The maximum altitudes along the heli-routes are always based on that setting (as is flight under the London TMA). Whilst under a service from Heathrow Special or Farnborough Radar) it would have been given to the pilot and read back as set, in this case before entering controlled airspace. His actual altitude would have been visible to ATC via the Mode C readout of his encoding altimeter.
He would have been given a maximum altitude to fly, not a minimum, which is the pilot's responsibility. The 1,000 foot rule would not be applicable, but the pilot still needs to comply with the 500 foot rule unless taking off or landing.
Twin engined helicopters do not necessarily have to fly along the river Thames and ATC may direct or clear the pilot to fly another route. The London heli-routes are mandatory routes for single engined but not for twins.