The helicopter - a Eurocopter EC 135, light utility, twin-engined machine with a 10-metre rotor disc - is small enough to get into the tightest of spaces.
It has the capacity for one pilot, two medics and one patient.
The MCRR is run by Dr Horan, who responded to his first emergency call-out in September 2015. Since then he has dealt with well over 150 emergencies.
"It's essentially 24/7," he told the Farming Independent.
"I'll specifically mark myself as 'unavailable' if I've got something on, but the rest of the time I am available to the Ambulance Service if they require my assistance."
With two small children, aged three and one year old, he says it's largely due to the support of his wife, Mary, herself a paramedic, that he can make this huge commitment.
"A couple of times, I've been in the middle of doing something like frying sausages for the kids or putting one of them to bed or brushing their teeth and got a call to go out.
"The calls tend to come in when I'm in the middle of doing something," he said.
At the same time, when approached by ICRR founder John Kearney to set up a unit in Mayo, he felt compelled to do it.
"I suppose it's always been an area of interest for me. My training is in emergency medicine and my interest is in acute care and dealing with emergencies and that's what my whole career has been.
"During my training I would have done extra time with the Ambulance Service and UCD, which runs a Graduate Diploma in Advanced Paramedics with the National Ambulance Service and Dublin Fire Brigade, and I worked as a clinical supervisor with them," he said.
Location also played a part in his decision to get involved.
"In Mayo there's only one hospital, in Castlebar, and there are quite long distances to travel. If I get a call in west Mayo or northwest Galway, chances are I'm going to be there before the Ambulance Service.
"There have been a couple of car crashes when I've been on the scene before the emergency services and the Gardaí. He believes it's a vital service in a rural area that is making a difference. By being there, he can start treatment on a patient before they leave the scene so they have had an hour of advanced treatment before they even get to hospital.
That life-saving treatment is often beyond the scope of practice of a paramedic.
He's looking forward to the day when the Irish Community Air Ambulance can further enhance this service nationally.
"The Galway helipad is the busiest in the country, used by the Athlone-based National Ambulance Service helicopter and the Coastguard helicopters in Galway and Sligo, and that demonstrates the need up here for the service.
"We've also got a number of islands, which aren't accessible by road, so definitely if there was a second helicopter in this area, we would find use for it," he added.
Like many of the volunteers, Dr Horan is pretty much a one-man show in MCRR, trying to organise fundraising and even the logistics of getting back home after an emergency.
"I'm busy enough with the day job and responding to the calls. I'm always looking for people to help - I think we would get a lot of support if we had someone to coordinate fundraising and run the events and it would be very welcome," he said.
John Kearney founded Irish Community Rapid Response in West Cork, following the avoidable death of the six-year-old daughter of a close friend, who died in transit to hospital. He's also the man behind the Irish Community Air Ambulance.
"All we do is provide them [the doctors] with the equipment. The work they do is phenomenal and what we do is make it possible for them to do that," he said.
A similar serviced, the Wales Air Ambulance, launched in 2001, completes around 2,000 missions a year. The charity's chief executive officer, Angela Hughes, was in Ireland recently to support the launch of the air ambulance.
She says the Wales service requires €6.5m to operate its four helicopters that service all of Wales and its population of three million.
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