What are your thoughts on using the bit before the displaced threshold to start the takeoff run?
DO.
This is quite common and normal. look at the definition of threshold - The beginning of that portion of the runway available for landing.
Take-off can be commenced from the start of the runway - see definition , or from the starter extension if one is provided.
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busidriver,
I still can not see a reasonable reason for you needing to land before the threshold.
You say that the published landing distance was suficient to permit commercial operations with your twin-jet. That means that your aircraft could land and stop within 60 percent of the landing distance publsihed in no wind if it is the only runway or in 50% of the headwind and 150% of the tailwind. All based on crossing the threshold at 50ft or 35ft if you are completing an approved short landing operation.
Even if you were to take it to the extreme and touchdown 1cm after the threshold, provided that the figures are as you say, I can not see how you would have to use excessive braking in order to stop in the available runway.
However, on a more serious note, since you specified "twin jet" you must be aware of the following from CAP382 - Mandatory Occurrence Reporting.
5.1 Applicability -
Any turbine-powered aircraft which has a certificate of airworthiness issued by the
CAA
Appendix B - Occurrences to be reported -
1.1
b) Take-off or landing incidents, including precautionary or forced landings. Incidents
such as under-shooting, overrunning or running off the side of runways. Take-offs,
rejected take-offs, landings or attempted landings on a closed, occupied or
incorrect runway. Runway incursions.
Landing before the designated threshold is under-shooting.
Regards,
DFC