Flying a helicopter without hydraulic boost can be an event that ranges anywhere from completely normal to life ending.
Fact is that some helicopters fly perfectly well without any hydraulic power to assist control inputs and some helicopters can not fly without them.Sikorsky sums up a total loss of hydraulics in one short sentence. “Flight is not possible” It doesn’t take a whole lot of imagination to realize that if you are flying these models of Sikorsky helicopter at the time of an improbable dual hydraulic failure you are going to have a bad day.
Somewhere in between no hydraulics installed and dual hydraulics where at least one system must be working, are the rest of the helicopters I have flown. Hydraulic systems are needed on most larger helicopters because of the control forces required to move the cyclic , collective and sometimes tail rotor.Pretty dull sounding stuff till you are struggling with a hydraulics off landing on a helicopter that probably should have been certified with dual hydraulics.
I have two rules when it comes to hydraulic failures on single hydraulic boosted helicopters. Number one, is don’t fly beyond your nearest suitable landing site. Some manufacturers list the emergency procedure for a hydraulic failure as land as soon as practical or practicable. My thought is don’t do it. Land. You don’t know what the problem is exactly. Land where you will not create a hazard to persons and or property and apologize later if you have to. You will at least be alive to apologize or defend your actions.
As instructors we teach hydraulic off emergency procedures and frankly some helicopters are very controllable without hydraulic boost. We can pick them up to a hover and maneuver around without hydraulics. Easy. The problem here is that, to a pilot new to the aircraft and possibly new to flying, he or she may walk away thinking that since the helicopter is easily controlled without hydraulics then losing hydraulics is no big deal.
That is wrong in my opinion.To all of you that questioned lifting off with hydraulics off in the scenario previously mentioned , good for you.I have had several FAA or FAA designated check airmen ask me to do that with a helicopter on a check ride. OK, but what emergency are we simulating ? My point here is that when we demonstrate hydraulic off emergency procedures we should also inform the student of the many secondary things that could be happening with the aircraft. If you have been flying helicopters for a few years and/or you are particularly well informed you can probably name several things that can appear as hydraulic failures and yet be something else or vice versa. Hydraulic failures can be mechanical, electrical,hydraulic and unknown. Most hydraulic systems are direct drive pumps. Hydraulic fluid in most helicopters has a relatively low flash point. The list goes on and on.
I prefer to land as soon as possible, every time. Would I fly past an empty football field to the airport a mile further. Maybe, but that is risk management and a P.I.C. ‘s lonely decision.
Rule number two for me is that I will not fly a single hydraulic powered helicopter that has any kind of secondary short term hydraulic boost system. When I see a back up surge tank or similar installed, the hair on the back of my neck goes up. Hydraulic systems of this nature are designed to provide enough back up hydraulic pressure to allow the helicopter to be landed after the primary hydraulic system has failed. Sometimes this secondary boost tank or system is to assist the main controls and sometimes to assist the tail rotor or both.
Either way, the manufacturer has cut corners by not installing a full redundant hydraulic system and recognizes that flight is possible without hydraulics but not advisable, or worse. Worse in that in a couple of models I have flown the lack of hydraulic boost makes the tail rotor pitch control “not possible ”
Some single hydraulic systems will lose their back up pressure just when you need them most . Do a run on landing in that case,as the manufacturer recommends or specifies as an emergency procedure. About 60 % of my time is spent where no place exists to make a run on landing anywhere.A run on landing where no place to run on and a hydraulic system that is about to become useless is a bad scenario. I’ll take that second fully redundant system now. Shame on you manufacturers and those that approved the helicopter to be certified without dual hydraulic systems when you knew that your decision may result in an accident.