An explanation of something I said in one of my recent YouTube videos.

I recently published a video on the FlyingMAir YouTube channel where I flew from my cherry season landing zone to my house. I was going to do a much longer flight that day with a friend and, when I reached the helicopter, I realized I’d forgotten my iPad, which I use with Foreflight for situational awareness and detailed airport information in flight. Faced with a choice of taking 20 to 30 minutes to drive back home and get it or just making the one minute flight up to my house on my way to pick up my friend, I went with the quicker option.

In the video, as I’m coming in for landing, I lament that a helicopter isn’t like a car and I can’t just keep it running while I go inside the house. I never explained why. A helicopter pilot — and even an airplane pilot — should know, but I forget sometimes that my video audience isn’t always directly involved in aviation. I got several questions — and a good story — in the video comments about leaving an unattended helicopter with the engine running. I thought I’d take a moment to share and expand on what was said in those comments.

First, Understand How a Helicopter Flies

The main danger of leaving a helicopter running while unattended is the possibility of it become airborne enough to move and crash. Never fear — if it does get airborne at all, it’s not going to fly away by itself. It will crash and likely pretty damn quickly. More on that in a moment.

The usual outcome of a helicopter trying to take off by itself is something like dynamic rollover, which is shown here. The helicopter gets hooked on something on the ground and rolls over. (This photo by John Murphy is from Wikipedia and used under the Creative Commons Attribution-Share Alike 2.0 Generic license. (Thanks, John, for sharing photos to help bloggers illustrate things like this.))

For a helicopter to get light on its skids and airborne, it needs a two main things:

• Rotor RPM. The main rotor(s) must be spinning. Theoretically, a Robinson can fly at 80% RPM plus 1% RPM per thousand feet of density altitude. So at my house on a warm summer day, I’d estimate 83% RPM would be enough to fly, although we always fly at 100% RPM (unless there’s some sort of in-flight problem that makes this impossible, in which case, we’d land as soon as possible). For this reason, it’s never a good idea to leave the rotors spinning at anywhere near 100% RPM unless the pilot is at the controls, paying attention and ready to fly.
• Collective Pitch. The collective control in the pilot’s left hand changes the pitch on the rotor blades the same amount (collectively) when it’s pulled up. With the collective full down, the blades are “flat” (or close enough for argument’s sake) and should not be able to get the angle of attack they need to produce lift. (And yes, the collective does look quite a bit like a compact car’s parking break lever.)

It’s the pilot’s responsibility to throttle down to an appropriately low RPM when on the ground. A Robinson’s cool-down RPM is between 60% and 70%; far too low for the helicopter to fly. When I flew at Papillon years ago, we’d just throttle down to the stop, which I think left us at around 70% RPM (but don’t quote me on that; it’s been 16 years). There are a few reasons why a pilot might not do this, but we don’t need to split hairs here because all of those reasons involve a pilot staying in the cockpit.

All the helicopters I know provide safety controls to prevent the collective from creeping up by itself. This is usually in the form of a collective friction lever (or possibly knob?) that the pilot should secure as part of her shutdown process. It becomes automatic. You set down, you throttle down to a cool-down or idle RPM (depending on your needs), and set the friction. Half the time, I don’t even remember doing it, but when I look down, it’s set.

So Is It Safe to Leave the Engine Running without a Pilot on Board?

Doing both of these things — reducing RPM and securing the collective in a full down position — should prevent a helicopter from misbehaving when parked when the engine is running. And lots of pilots will actually walk away from a helicopter with the engine running. Let me elaborate.

Suppose I was sitting in the helicopter with the engine running and I realized I needed something out of the back seat storage area. I need to get out to fetch it. Would I shut down?

The answer is no. I’d start by confirming low RPM and secured collective. Then I’d take off my headset and seat belt, open my door, climb out, open the back door, fetch what I needed, close the back door, and get back into my seat. During that entire time, I’d be well within reach of the controls if I started to hear or feel something weird going on.

Likewise, when I worked at Papillon, they’d routinely land a Bell 206L in the Native American village of Supai at the bottom of the Grand Canyon. The pilot would throttle down and secure the collective, then get out, walk around the front (never back!) of the helicopter, open the luggage compartment, and pull out luggage for the departing passengers. (That was back in 2004; I have no idea if they still do this but assume they do. It makes sense given the possibility of restarting difficulties without a ground support crew/equipment.)

Meanwhile, up at the Grand Canyon South Rim base, if a pilot needed to use the bathroom between flights, he’d have to wait until another pilot came down and sat in his seat until he returned. No passengers would be loaded during this time. This was a smart safety measure that some folks might consider overkill. I don’t.

A friend of mine who owned an R44 started up his helicopter on the ramp of his home base airport, which, at the time, I believe was Salinas in California. As he was warming up the engine, he realized he was missing a chart. Rather than shutting down, he simply left the helicopter empty, idling on the ramp, while he went to the on-airport pilot shop and bought the needed chart. He got into a ton of trouble with airport management when an airplane pilot complained about it. Friend or not, I think he exercised poor judgement when he did that.

The Story in Comments

One of my YouTube channel’s commenters, George Reynolds, had this to say about my video:

Not like a car, leaving the engine running. Reminds me or a true accident report where the pilot landed beside a house to impress a friend and got out, leaving the 3 forestry workers in the helicopter with the engine running. One of them thought the “handbrake” ought to be applied and the consequences was a wreck, but fortunately no injuries….

My first thought was OMG, what a story! It’s a perfect example of what can happen when a pilot fails to properly brief his passengers.

Going back to my original situation, if I had a responsible adult passenger in the front seat when I landed at my house, I’d throttle down, secure the collective, and advise the passenger to leave the controls alone, especially the collective, which should not be raised under any situation. Then I’d feel comfortable enough leaving the engine running.

What Could Happen

George’s story sent me to the NTSB database to look for the accident in question. I searched using all kinds of key words based on his story: handbrake, brake, house, passengers, pulled collective. I did not find a single story that matched.

But I did find others. Here are a few summaries; emphasis added:

Accident report LAX97FA149 on April 7, 1997 in Los Angeles, CA tells this story:

The pilot exited the helicopter to escort a deplaning passenger. The student pilot rated passenger was left sitting in the helicopter with instructions not to touch the controls. While the pilot was standing nearby, the helicopter began bouncing up and down in a resonant mode. The pilot ran back to the helicopter and pulled the fuel flow control lever into the cut-off position. The helicopter yawed to the right and settled back on the deck. Investigation revealed the full down position of the collective was spring loaded to keep tension against the control lock. An inspection of the helicopter revealed that the collective was not down and locked, nor were the frictions tightly applied. The manufacturer reported instances in which the collective lock was not seated properly, and consequently, the collective became released while the engine was running. If the lock slips off collective, the spring’s tension could force the control to move upward. No malfunction or failure was found with the engine or rotor systems.

So either the pilot hadn’t locked the collective or the collective lock had released due to a known design flaw.

Accident report LAX07CA034 on November 11, 2006 in Boulder City, NV says:

The helicopter rolled over after the pilot exited with the engine running and rotors turning to disconnect and move the auxiliary power unit (APU) to a secure location. The pilot left the helicopter running at 100 percent because he was charging the battery. The pilot’s back was to the helicopter when he heard the engine sound change. He turned around, and saw the front skids lift off the ground. The helicopter started to move in a backwards direction, and rolled over and went down an embankment.

Sorry, folks, but this is a stupid pilot trick, plain and simple. Never leave the helicopter at 100% RPM when there’s no pilot at the controls.

Accident report LAX01FA252 on July 21, 2001 in Los Angeles, CA reports:

The pilot got out of the helicopter with the engines running and the rotors turning to check on the security of a cabin door, and the unmanned helicopter began moving on the helipad and rolled over. The pilot had completed a nightime, helicopter, air taxi flight, and was preparing to depart the elevated helipad to reposition the helicopter to the operator’s base. After deplaning his passengers the pilot returned to the cockpit and was preparing to depart when he noticed a door unsecured indication on the instrument panel for the left cabin door. The passengers had deplaned through the right-hand door and the left door annunciation had not been on during the inbound flight. He thought one of the passengers might have released the left door latch inadvertently while preparing to deplane. He idled the engines and exited the cockpit to check the door. He reclosed the door and returned to the cockpit; however, the door open annunciation came on again. He recalled leaving the cockpit “2 or 3 times” to deal with the door and said he was “frustrated with it.” He did not recall retarding the engine power control levers to ground idle before leaving the cockpit the final time. While out of the cockpit, the wheel-equipped helicopter started to move as the pilot was returning to the cockpit. He recalled it was moving toward the edge of the helipad. He returned to the cockpit; however, before he could regain control there was a confusing sequence of events and the next thing he knew the helicopter was on its side. The pilot reported there were no mechanical discrepancies with the helicopter up to the time of the event. He remarked that it was very light [weight] with no one else on board. On the deck of the helipad there was a tire skid pattern consistent with a dynamic rollover event. The engine power control levers were found in the “fly” position.

I really feel for this guy. Something is acting up, giving him grief, and he’s frustrated. Unfortunately, that can also make you sloppy. I don’t know much about Sikorsky S-76 helicopters and nothing about the “fly” position, but I have to think that a helicopter should be set to “fly” when the pilot intends to fly. Maybe someone reading this can fill in more details? Since the chances of me ever flying an S-76 are very slim, I’m not interested in researching it.

Why This Matters

I’m a student in the School of Thought that says the more you know about what could happen, the better equipped you are to make smarter safety-related decisions.

In my video, my landing zone was good, there was little or no wind, the collective friction on my helicopter works fine, and I could have throttled all the day down to 60% RPM if I wanted to. The chances of the helicopter moving an inch while I was in my house were nearly zero.

Nearly.

There’s always a chance that something unexpected will happen. Having lost one helicopter already, I’m not interested in losing another. So I do what I think is safe, even if other folks think it’s overly cautious.

If the folks in the four accident stories I shared here had been students in the same School of Thought I’m in, their stories wouldn’t need to be shared.