How long from power-down to power up?

[nicepants]

I work across the street from a trauma center, with helicopters coming & going on a daily basis. Today I noticed one that came in, shut down, and powered up/took off less than 20 minutes later. I had a couple of questions about this:

 

1 - For EMS...is it required that the ship be completely shut down & rotors stopped before loading/uloading a patient?

2 - For anyone else, is there a minimum time you typically have to wait before starting back up to avoid turbine problems?

 

FWIW: The a/c in question was a BK 117.

Edited September 21, 2007 by nicepants

[Mike Murphy]

The time is generally based on the turbine gas temperature. Most aircraft require it to be below a certain value for engine start and/or water washes. If we were close we would just motor the engine until the TGT was below limits then introduce fuel...just be ready to modulate the start and watch for a hot one!

Edited September 21, 2007 by Mike Murphy

[arotrhd]

"For EMS...is it required that the ship be completely shut down & rotors stopped before loading/uloading a patient?"

 

On loading side: if it's a patient transfer, you'll be shutting down on both ends (paperwork and the patient is usually quite stabilized). For scene calls, it all depends on patient condition (extracted? packaged? patient weight and load capabilities...), agencies involved on scene, overall comfort level, and hazards/risks within or near the LZ. Often the radio reports inbound will give some hint; the Pm or nurse will do an eval/assessment and verify or announce some surprises relating to the ride out for the patient...might not be a big deal if you're in a 412, but could mean somebody is staying if it's a L3. Sometimes the helo might have to drop the med crew and depart for a few minutes to burn some fuel if it's a case of overweight patient or multiples. It all depends...coordination + comms are vital.

 

On the off-load: generally, the helicopter is shut-down and secured prior to patient movement outside of the aircraft (for civilian airmed). However, there are a few instances or large events (i.e., disasters - Katrina) when a hot offload is requested or desired; if the pad/LZ is clean and clear, the ground staff uses appropriate approach paths to the cabin and all the patient leads/lines/bags/monitors are secured (including patient or patients), items in the cabin are stowed/secured, and everyone is thumbs-up, it shouldn't be a big deal. But it's not the preferred standard method due to safety considerations and unnecessary risk exposure for all personnel involved. FOD, loose items, environmental factors (ice or slick decks) and people who don't have good orientation around the aircraft in these situations aren't the best combinations 'while the rotors are turnin and cans are burnin'.

 

-WATCH FOR THE WIRES-

[Gomer Pylot]

It depends. Most hospitals prefer cold offloads most of the time, but may require a hot offload if there are multiple helicopters inbound. We take what we get from the hospital. A turbine can be restarted at pretty much any time, but you have to watch the temperature - TOT, TIT, T5, or whatever it is referred to for that particular engine. You may have to motor the engine with the igniters off to cool it down before the start, or let the N1 build up slightly higher before lighting it off. Experience helps here.

[Wally]

Like the man says, it all depends. In the Astar, with the Turbomecas and their 30 second temperature stabilization, it's quicker to shut down and restart after loading the patient. It's more efficient because there are fewer distractions and easier communications, safer and all around less stress. And, the Turbomecas are tolerant of quick restarts and easy to modulate.

My program also has an Rolls-Royce/Allison engined-Astar, and it's different beast. The RR/Allison engines have a 2 minute temp stabilization, don't like quick restarts (depending on OAT and winds 15-30 minutes), and are more work to modulate. A quick restart with a warm Allison can be "dramatic", I've had them light-off with significant sound effects...

I can't think of a turbine engine that CAN'T be quickly restarted- at least the ones with pilot modulated starts. In fact, it has some advantages, if you know what to be careful of.

[Gomer Pylot]

I had rather restart an Allison immediately than wait 5 or 10 minutes. The temp goes up as it sits, and as you said, there can be some sound effects, especially from a B model. I never liked those. The D model AStars, with the Lycomings, started very mildly, even when hot. I agree, if you know what you're doing, and are ready, you can get a start out of almost any engine, even with a weak battery, at least most of the time. You really have to be careful of a hot engine and a weak battery, though.

[arotrhd]

Good points Gomer & Wally.

 

-WATCH FOR THE WIRES-