Tag Archives: FAA

Flying in a Heat Wave: Safe? Legal?

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I explore the logic behind performance charts and what the FAA told me about flying in hot weather.

Upcoming Weather
Next week’s weather. It’s going to be hot.

I have a Part 135 check ride coming up on Tuesday. Per the National Weather Service — my primary source of weather information — the forecast high in Wenatchee for that day is 112°F.

If you live in any country other than the metric-unfriendly US, that’s 44.4°C.

IGE Hover Chart
The IGE Hover Chart for an R44 Raven II does not chart any performance data for temperatures above 40°C.

The In Ground Effect (IGE) Hover charts for a Robinson R44 Raven II, which is what I fly, end at 40°C. That is, they do not provide any performance data for 44.4°C.

Now I learned to fly in Arizona and on a typical summer afternoon, 112°F was not uncommon. We flew in all kinds of heat. Hell, I remember landing at Bullhead City one day and reading 123°F on my outside air temperature (OAT) gauge. (And that was in a helicopter without air conditioning.) If the flight school I attended — which is still in business — didn’t fly when it was above 104°F (40°C), they wouldn’t be able to fly half the day about a third of the year. No one questioned whether it was safe or legal. We just did it.

Time went by. Someone suggested to me that flying when the temperature was above 40°C was not only unsafe but illegal. “You’re a test pilot when you do that,” more than a few people have told me. “Your insurance wouldn’t cover you in a crash,” another said, “because you’re operating outside of published data.”

Curious to see what other pilots thought about this, I put a poll on Twitter and gave the Pilots of Twitter 24 hours to respond. I also asked for comments. A lively discussion got going in the comments. It was also pointed out that I could have added “Unsafe but legal” as one of the options with the shared opinion that “the FAA gives you enough rope to hang yourself with.”

I do recall airplanes being grounded at Phoenix Sky Harbor airport one day when temperatures were “too hot” for some of the airliners, although it wasn’t clear from articles I read about how the limit was established.

Well, in an effort to head off a “gotcha” by my FAA examiner, I emailed him this morning to warn him of the heat:

A quick heads up.

We’re expecting high temperatures of 112°F on Tuesday. If you are of the school of thought that says we can’t fly when temperatures exceed 104°F because that’s the highest temperature on performance charts, we should probably plan to fly very early, before the temperature tops out. …

If you’re not of that school of thought — I learned to fly in Arizona so I’m not — we should be fine. The helicopter does have air conditioning, although I’ve never tested it in 112°F weather.

Please let me know what time you plan to arrive.

He replied, in part:

I am unaware of a temperature limitation that restricts operations of the R-44. We can complete the ground during the afternoon of the 28th so we can fly on the morning of the 29th to minimize the effects of the heat. …

So that’s telling me that it’s legal. (But he’s not taking any chances or doesn’t want to test my air conditioning.)

Never Exceed Speed
Here’s a limitations chart: Never Exceed Speed. If I extrapolated, I think operations at lower elevations would be fine, but I certainly wouldn’t exceed about 85 knots 44°C at 8000 feet. (Heck, the helicopter would be vibrating like crazy at that speed and elevation anyway.)

Is it safe? Well, as this “test pilot” could tell you, if you extrapolate the data in the charts, keeping in mind the aircraft’s gross weight and the altitude you would be operating at, it can be. Keep the aircraft light, don’t plan any high altitude landings, and keep your speed down.

Chances are, the helicopter will continue to operate in heat that you won’t want to be flying in anyway.

Why Helicopters Don’t Normally Take Off Vertically

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Just because you can do something, doesn’t mean you should do it.

Every once in a while someone watching one of my YouTube videos or searching for answers on the web that bring them to this blog ask why helicopters don’t take off straight up. I guess these folks know that it’s possible and they’ve seen it often enough in the movies to think that it’s normal or at least okay. It’s neither.

I actually explain why in my much longer post about the Deadman’s Curve. But I’ll try to keep it simpler here.

The Basics

Let me start off by saying that helicopters can glide. Yes, if the engine fails, the pilot still has control over the helicopter and can fly it, using autorotation, to the ground. If conditions are right and the landing zone is appropriate and the pilot’s skills are sufficient, the pilot and passengers should be able to walk away and the helicopter might even be able to fly again.

Notice that I mentioned three ifs:

  • if the conditions are right
  • if the landing zone is appropriate
  • if the pilot’s skills are sufficient

Height-Velocity Diagram for R44 HelicopterIt’s that first if that the pilot usually has complete control over: the conditions of flight. That’s where the Height-Velocity Diagram comes into play. This diagram, which is part of the Pilot Operating Handbook (POH) that pilots are required to know inside and out (and even carry on board, as if we could consult it while flying), shows the flight profiles in which an autorotation is most likely to be completed successfully. By “flight profiles,” I’m referring to a combination of airspeed and altitude.

To meet the requirements of that first if — in other words, to fly the safest flight profile in the unlikely event of an engine failure — the pilot needs to stay out of the shaded area of the Height-Velocity Diagram. A recommended takeoff profile is shown on this chart by a dashed line that starts at 0 knots and less than 10 feet off the ground, accelerates through 45 knots while climbing less than 15 feet, and then climbs out at a speed greater than 50 knots.

Make a mental picture of that. If you’re not going to climb above 10 feet until you get to at least 30 or 40 knots, are you going to be flying straight up? No. You’re going to be taking off a lot like an airplane might, with a bunch of forward movement before you start climbing.

This is why a “normal takeoff” for a helicopter climbs out after gaining airspeed — instead of climbing straight up. It’s for safety reasons.

(This is only part of the reason why we don’t land straight down, but I’ll save that for another blog post if I get requests for it.)

FAA Guidance

The FAA has a wealth of free information about flying, including “handbooks” that explain exactly how to fly. I’ve linked to the Helicopter Flying Handbook many times; if you don’t have a copy of this excellent guide and are interested in flying helicopters, download it in PDF format here.

Here’s what it says about performing a normal takeoff from a hover (position 1 in the image that follows) on Page 9-12:

Start the helicopter moving by smoothly and slowly easing the cyclic forward (position 2). As the helicopter starts to move forward, increase the collective, as necessary, to prevent the helicopter from sinking and adjust the throttle to maintain rpm. The increase in power requires an increase in the proper antitorque pedal to maintain heading. Maintain a straight takeoff path throughout the takeoff.

While accelerating through effective translational lift (position 3), the helicopter begins to climb, and the nose tends to rise due to increased lift. At this point, adjust the collective to obtain normal climb power and apply enough forward cyclic to overcome the tendency of the nose to rise. At position 4, hold an attitude that allows a smooth acceleration toward climbing airspeed and a commensurate gain in altitude so that the takeoff profile does not take the helicopter through any of the cross-hatched or shaded areas of the height/velocity diagram. As airspeed increases (position 5), place the aircraft in trim and allow a crab to take place to maintain ground track and a more favorable climb configuration. As the helicopter continues to climb and accelerate to best rate-of-climb, apply aft cyclic pressure to raise the nose smoothly to the normal climb attitude.

Normal Takeoff
This is an exaggerated view. In reality, each position would be a lot farther apart horizontally.

In the above text, in an R44, effective translational lift (ETL) occurs between 15 and 25 knots, normal climb power is about 45 knots, and then climb out power (best rate of climb) is 60 knots. So you basically stay within 10 feet of the ground until you’re at 45 knots, then accelerate while climbing to 60 knots, and then climb out at 60. These numbers may be different for other aircraft but are likely similar.

Real Life Situations

Watch My Helicopter Videos on YouTube

Time for a shameless plug…

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If you like helicopters, you’ll love the FlyingMAir YouTube Channel. Check it out for everything from time-lapse annual inspections to cockpit POV autorotation practice to a flight home from a taco dinner at a friend’s house — and more.

Of course, one of the benefits of helicopters in many operational situations is that it can fly straight up. For example, I can take off from a confined space — perhaps a forest clearing — by being able to climb up above obstacles (the trees around me) before picking up airspeed and flying away. Is this safe? Well, there isn’t any signifiant danger unless the engine quits. And although the chances of the engine quitting are very slim, it is possible.

Years ago, while doing a rides event at the local airport with some fellow pilots who were working with me for cherry season, I noticed that one of the pilots was departing our landing zone by climbing straight up for 20 or 30 or even 50 feet before gaining airspeed. He was putting the aircraft right in the shaded area of the Height-Velocity Diagram. In other words, he was adding risk to his flight by basically ignoring the recommended takeoff profile.

With passengers on board. At a crowded event.

I’ve got a pretty good imagination and was immediately able to “see” what could happen if his engine quit. The helicopter would drop down with its blades still spinning. Everyone on board would likely be killed or seriously injured. And when all those spinning parts hit the ground and started flinging off in every direction, they’d likely kill or injure dozens of onlookers.

What were the chances of his engine quitting? About as close to zero as you can get without being zero. But that isn’t zero. It could happen.

After seeing him do this at least four times and realizing he wasn’t going to stop, I got on the radio and told him to stop. He asked me why. Knowing that I was talking on a frequency that could be heard by his passengers, my passengers, any other aircraft flying around the area, and anyone monitoring on the ground, I kept it simple: “Just because you can do something doesn’t mean you should.” I let him think a bit about why he shouldn’t and he stopped. (If he didn’t, I would have kicked him out of the event.)

Over the following month or so, I got to know this pilot better and I didn’t like what I saw. I don’t need to go into details here, but I feel that he’s the kind of pilot who will likely get himself killed doing something dumb in a helicopter. I’m just glad I took steps to make sure it didn’t happen on my watch.

Question Answered?

If this doesn’t answer the question about why helicopters don’t take off vertically, I don’t know what could. Please don’t hesitate to share your questions, comments, and stories in the comments for this post. Thanks!

Helicopter Minimum Altitudes

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I’m working on a much longer blog post, with photos, about my recently completed autumn vacation, but I thought I’d put this shorter post out because it’s quick and on my mind.

It started with someone on Twitter sharing a video from inside the cockpit of a helicopter flying low and fast over a forest road. There were no cars on the road and no poles or wires. It was an exciting little flight that reminded me of the kind of canyon flying I used to do in some very familiar, remote areas of Arizona. See for yourself.

Helicopter video screenshot.
Here’s a screenshot from the video in question.

What followed was a bunch of comments, including some from a few people too lazy to look up the regulations who claimed that flying like that was illegal. When I pointed out that it was not illegal in the US, a particularly lazy, uninformed idiot quoted my tweet with a portion of the FARs in an attempt to prove me wrong. He didn’t. All he proved is that like so many people these days, he’s only capable of reading until he gets confirmation of what he wants the truth to be. The rest doesn’t matter.

Here’s the entire FAA regulation covering minimum flight altitudes in the US:

§91.119   Minimum safe altitudes: General.

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:

(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.

(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.

(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

(d) Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface—

(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and

(2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section.

[Doc. No. 18334, 54 FR 34294, Aug. 18, 1989, as amended by Amdt. 91-311, 75 FR 5223, Feb. 1, 2010]

Did you read paragraph (d) and paragraph (1) right beneath it? I did, but the know-nothing twit pretending to be an expert on Twitter didn’t. It basically says that the paragraphs he quoted (paragraphs (b) and (c) above) don’t apply to helicopters.

I distinctly remember this FAR coming up during my primary training back in the late 1990s. It basically gives helicopter pilots permission to fly at any altitude they need or want to, given that “if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.”

Take a look at the video. It looks to me as if the pilot is 50-100 feet off the ground. He’s moving at a good clip — at least 60 knots. (I tried to read the airspeed indicator but couldn’t.) With that altitude and airspeed combination, he’s not operating in the shaded area of the height/velocity diagram (or “deadman’s curve“). That means that a safe emergency landing is possible. And with nice smooth pavement beneath him, there’s plenty of suitable space for a landing if it was necessary. So it’s not in violation of paragraph (a) either.

Watch My Helicopter Videos on YouTube

Time for a shameless plug…

Flying M Air Logo

If you like helicopters, you’ll love the FlyingMAir YouTube Channel. Check it out for everything from time-lapse annual inspections to cockpit POV autorotation practice to a flight home from a taco dinner at a friend’s house — and more.

Lots of people don’t get this. They assume the altitude rules apply equally to all aircraft. But they don’t. This makes it pretty clear. Trouble is, there are too many self-important assholes out there — especially on Twitter — who share inaccurate or incomplete information as fact — and too many lazy people willing to believe them without doing their own homework.

If you want to read more about this topic, here’s an old, long, rambling post I wrote about an experience related to this years ago.

Oh, and by the way, this post is about whether the flight is legal in the US. I won’t make any comments about whether it’s safe or whether the pilot is using good judgement. That’s a whole different topic.