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By Randy Mains “BUT ALL TWINS ARE NOT ALIKE”


I SAID TO THE AIR MEDICAL FLIGHT DOCTOR


WHO IS


AIR MEDICAL AMERICA


VERY


TO MAKE IT MANDATORY ALL IN


OPERATE


KEEN THAT


PROGRAMS TWIN-


ENGINE HELICOPTERS. HE REPLIED, “I WASN’T AWARE OF THAT.”


So, what are the differences? It all has to do with the weight-to-horsepower ratio of the machine and the ability to either land safely on one engine or fly away.


Helicopters are categorized by the FAA as Performance Class 1, 2 or 3.


Performance Class 1 is defined as those helicopters with performance such that, in the event of failure of the critical power unit, the helicopter is able to land within the rejected take-off distance available or safely continue the flight to an appropriate landing area, depending on when the failure occurs.


To be operated in Performance Class 1, a helicopter must be certified in Category A, which is a design requirement meaning it must be equipped with at least two engines, and also have a certain number of safety-related equipment items, as well as redundant backup for control, lubrication, etc. Category A helicopters must offer the performance needed to guarantee that, in case of an engine failure, the flight can continue safely.


Under Performance Class 1 conditions, the helicopter can manage the failure of one of its two engines at any given moment while maintaining satisfactory safety


criteria, 8 especially takeoff or landing phases. May/June 2017 during the


Performance Class 2 is a helicopter also certified Category A, but a certain “exposure time” to the engine failure is allowed. When the engine failure occurs


early during takeoff, or late


during landing, a forced landing may be necessary depending on power available from the remaining engine. What that means is Performance Class 2 offers a lesser safety guarantee than Performance Class 1. However, if the failure should occur in flight, the helicopter’s performance means that it can still continue the flight as long as it is not too high or too heavy to overwhelm the remaining engine.


Performance Class 3 helicopters are such that in the event of a power unit failure at any time during the flight, a forced landing may be required in a multi-engine helicopter (Think heavy helicopter where the ‘good engine’ does not have the horsepower to keep it aloft) but will definitely be required in a single- engine helicopter.


Category A means multi-engine helicopters with engine and system isolation and Flight Manual performance based on a critical engine failure concept


providing adequate area and performance capability


surface for


continued safe flight if an engine fails. In other words, in addition to making sure you have power available (by restricting maximum


all-up takeoff weight, it


provides space for rejected takeoffs and landings, and obstacle clearance.


Category B means single- or multi- engine helicopters not fully meeting Category A criteria. They are not


On the night of January 26, 1982 I was flying an Alouette III in the mountains east of Miramar Marine Air Station in San Diego on a HEMS mission trying to find my way up valleys in low cloud. I decided that the weather was too bad to continue and called our hospital dispatch to say we were turning around.


I dialed up the Miramar frequency to inform the tower controller we were going to re-enter their airspace. He came back with an urgent request saying he had an H-61 (Sikorsky) helicopter in trouble saying that one of its engine’s had exploded and the aircraft couldn’t maintain altitude on the good engine, that he was in a slow descent into the mountains and that the pilot didn’t know his exact position. He told me, “He’s too low for us to pick him up on radar. Can you see if you can find him?”


I began a turn back into the mountains and bad weather, and transmitted, “Roger Miramar, I’ll see what I can do. Any idea where he might be?”


The controller gave me a radial and distance from the Julian VOR. I did a quick mental calculation and turned on a heading back into the mountains to see if I could spot him.


It was extremely dark and the weather wasn’t any better than when I turned around last time. These were the days before NVGs so I could only just make


guaranteed to stay airborne if an engine fails and an unscheduled landing is assumed, possibly with some damage. Here’s a good personal example:


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