Hello,
As I had a chance to observe several police and HEMS/SAR operations (and am working for one) I am humbly putting forward my observations:
in Austria, OAMTC crews, flying EC 135s with Pilot and HEMS crewmember and doctor on board. (Swiss REGA works similar way)They regularly take off within three minutes ( not a required standard!) when weather is not an issue and flight is within designated operating area, which is fairly small for each base (about 50km circle). They have carefully prepared procedures -and also hardware, like crew quarters are only a few steps away from helicopter, movable helipad(on rails) allows single person to push helicopter out of hangar in half a minute, etc.
Helicopter, weather, medical stuff etc. is checked and prepared in advance and regularly updated-rechecked, no one except crew has acess to helicopter on duty, etc. Even kitchen could be modified - imagine coming back from a mission, finding burning home base, as someone left pan full of cooking oil on cooking plate!
As soon as request for takeoff and location is received, pilot goes out, doing start up. HEMS crewmember, responsible for tactical navigation, comes later with the details of destination, situation, etc.
I had a chance to fly with several UK police helicopters - mostly liftoff occoured in about 3 minutes after phone rang. Shortest scramble I witnessed was 1min 45 seconds from bell ringing to liftoff - and I swear, I never witnessed any rush - everything going on smoothly, as it was done thousand times before on a predetermined procedure, that was developed and finessed out thru experience.
Even big Bristows S61N SAR I had a privilege to fly aboard, was airborne within 5 minutes if needed. Everything prepared, special checklists in use, a lot of proffesionalism, and there never was any rush - everything went smoothly, but with no delay. Mind that crew has to put on immersion suits too!
Flew with RAF SAR Sea King too, but response time was a bit longer - also due to the fact that crew quarters were far away from helicopter, so a van was used to get there.
Where I fly, we regularly take off with Bell 412 in 5 - 6 minutes after the call, if weather and mission planning is not an issue. If there are doubts, it can be 10 or 20 minutes - until pilot, or better say, crew is happy with the decision to go. Still, preflight checks are done and myself as crewchief am doing final walkaroud when engines are already running - we caught two hydraulic leaks in the last two years this way. It is an added bonus, that crewchief is most of the times also licensed engineer, so snags can be often sorted out quickly.
In my humble opinion, short take off times (3-5 min) can be achieved safely under certain conditions, but the whole organisation must be adapted to such operations - including outfit of hangar, communications, crew quarters, personal equipment (boots with zippers, for instance,) etc.
If you approach this issue with "airline" or "Point A to point B transport of medics and patients" thinking, you will either achieve unacceptable scramble times, or you will skip safety. Truly, few seconds will hardly mean anything to a patient condition, but in rescue/HEMS business (also police ) there could be a big difference between 5 and 15 minutes takeoff time on final outcome, not to mention the decision to take off at all. Agree that there is no point in trying to catch some predetermined takeoff times, not only from the safety point, but also from the patient point - there is no sense in trying to reach that patient, only to tell the medics, waiting with him, that you cannot reach them - time lost that could be used to move patient with ground transport. It is even worse, to load the patient and then try to figure out where to deliver him, as planned destination hospital is out of reach due to storm that just developed.
Stay safe!
