The Deadman’s Curve

Why helicopter pilots balk when asked to hover at 50 feet.

Last year, I joined a listserve group of professional aerial photographers. These folks, who are based all over the world, have been working at their profession for years. I’m a relative newcomer to the aerial photography scene and arrive as a pilot — not a photographer. (I want to take photos, but it’s tough when my right hand is stuck holding the cyclic during flight.)

I introduced myself and an engaging conversation about flying helicopters ensued. As you can imagine, many of the photographers had worked with helicopters. One of them was even on board during a crash!

One of the photographers in the group told a story about photo flights he’d taken with helicopter flight school instructors. He included this comment:

I was shooting a lot of sailboat races at the time, so where I wanted it turned out to be in a hover at 20 to 50 feet above the water which made some of the instructors nervous. I told them to get over it.

A lot of pilots won’t work in what’s commonly referred to by helicopter pilots as the “deadman’s curve.” All helicopter pilots should know what this is, but here’s a brief explanation for those of you who aren’t familiar with helicopter flight.

The “Deadman’s Curve”

Height-Velocity Diagram for R44 HelicopterThe Height-Velocity diagram in the pilot operating handbook (POH) shows the combinations of airspeed and altitude at which an experienced pilot (or test pilot) should be able to make a safe autorotation in the event of an engine failure.

The diagram shown here is for a Robinson R44 helicopter, but they’re all very similar. The idea is to stay out of the shaded area. Generally speaking, you want either altitude or airspeed — or (preferably) both. Hovering at 20 to 50 feet puts you in the “deadman’s curve” — it’s a combination or airspeed (0 knots) and altitude (20 to 50 feet) at which a safe autorotation is not possible. So if the engine quits, you’re dead.

The height velocity diagram also clearly shows the recommended take-off profile. When a pilot does a “by the book” take-off, this is what he’s doing: picking up into a hover less than 10 feet off the ground and accelerating through 45 knots. Then pitch up slightly and climb out at 60 knots. (You can get an idea of this in my “Shadow Takeoff” video.) Doing a “straight up” take-off like you see in the movies or on television puts the helicopter smack dab in the middle of the deadman’s curve until he’s moving faster than 50 knots or has climbed several hundred feet.

Wondering how the chart is created? With test pilots and helicopters. If you take the Robinson Factory Safety Course, you’ll see videos of the flights they used to build the chart — including one flight that demonstrated what happens when you attempt an autorotation while inside the deadman’s curve.

My Experience with the Deadman’s Curve

I get some photo gigs because I’m willing to operate in certain areas of the deadman’s curve to meet my client’s needs. I’m a single pilot operator so I’m responsible for myself. Other organizations are responsible for their pilots and tell their pilots not to do anything that could be “unsafe.” This is often the situation at flight schools that do photo flights for extra revenue. Those pilots are usually the school’s CFIs, sometimes with only a few hundred hours of flight time. The school makes a rule — no operations under 300 feet — and all the pilots are required to comply.

Operating in the deadman’s curve requires that you have a lot of confidence in your engine and mechanic. The engine failure statistics on Robinson helicopters show that the engine — a Lycoming, after all — is very reliable. And I take meticulous care of my aircraft with two experienced mechanics to do the work. I’m confident in my aircraft. So I take the risk and I get the job.

But I do warn my passengers of the risks inherent in that type of flying. And If a maneuver puts me too close to obstacles or requires me to do something I think is beyond my skill level, I won’t do it. (I don’t have a death wish.)

Get Over It?

“Get over it,” is a pretty funny thing to say to a pilot when requesting (or demanding) that he perform a maneuver he’s not comfortable with or authorized to do.

The pilot who balked at hovering 50 feet off the ground was doing it for safety — his and his client’s. The photographer who told him to “get over it” was unfair to expect the pilot to operate where he was not comfortable. At the same time, the pilot should have clearly stated the limitations of the flight before accepting the job so the photographer wouldn’t expect the pilot to perform maneuvers beyond his normal operating scope.

Unfortunately, more than a few pilots will simply cave in under pressure to please the client. Sometimes this is can be a very bad thing that both the pilot and his client don’t live to regret.

A good pilot will evaluate the risks, make a decision, and stick to it. A pilot who is easily bullied by passengers (or management, for that matter) needs to look for a new career.

Misleading Statements in Popular Fiction

I actually wrote most of this post months ago and mothballed it to finish at a later date. But yesterday, I read something in a novel that made it clear how little the general public understands about helicopter operations.

In the story, the protagonists are passengers on a helicopter that’s running out of fuel. The lead protagonist tells the pilot to lose altitude. His reasoning:

Helicopters sometimes survived engine failures at a few hundred feet. They rarely survived at a few thousand.

The above statement is false. Reverse the facts and you get the correct statement, which I could word like this:

Helicopters rarely survived engine failures at a few hundred feet. They usually survived at a few thousand.

Why the difference? The H-V Diagram is a big part of it. Take a look. If a pilot is flying at 200-300 feet, he’ll have to be moving at at least 50 knots to stay out of the deadman’s curve. The H-V Diagram clearly shows that the higher you are and the faster you go, the farther you are from the deadman’s curve. Altitude and airspeed are two energy management components that can save a pilot’s life in the event of an engine failure.

If you’re operating outside the deadman’s curve, the thing that makes higher altitudes safer is time. If you’re cruising along at 500 feet AGL at 100 knots — a perfectly safe combination of altitude and airspeed, according to the H-V Diagram — you’re going to be on the ground a lot quicker than if you were doing the same speed at 1,500 feet AGL. That’s less time to correct any problems with your autorotation entry, pick a good landing zone, make a Mayday call, brief your passengers, etc. Now imagine cruising at the unlikely altitude of 3,000 feet AGL. In a good gliding helicopter, like my R44 or a Bell LongRanger, you have lots of time to set it up and do it right.

Clearly, higher is better.

There were some other errors in the book as far as the helicopter was concerned, but I’ll save them for another post. (It really does bug me when books, movies, and television send inaccurate messages about how helicopters fly.)

Why Not Get the Facts Straight?

Time passes. I don’t recall when I started writing this post, but I know I didn’t last long with the photographers in that group. They were very full of themselves and highly critical of newcomers. And some of them echoed the same uninformed ideas about the safety of helicopters that I hear everywhere else. Worst of all, they didn’t seem interested in learning the truth.

I wrote a post earlier this month titled “Why Forums Suck” that describes the atmosphere in this particular group. Maybe it’s me, but I simply don’t have patience for people who behave the way some of these guys (and women) did.

And, in case you’re wondering, I e-mailed the author of the book with the errors. I hope he didn’t think I was being rude. But I want him — and anyone else preparing material about helicopters — to get the facts straight before releasing it to the public. In his case, any helicopter pilot could have pointed out the problems I found and reported to him. A few minor changes to the manuscript would have made it accurate without impacting the story one darn bit.

I just wonder if other pilots who read the book were as irked about the errors as I am.

Probably not.

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~ by Maria on April 27, 2008.

One Response to “The Deadman’s Curve”

  1. Thanks for the Lynda videos. WordPress was a little overwhelming for me, even though I’ve been designing website for a while.

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