Tag Archives: FAA

Unanticipated Yaw

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Some comments about one of Robinson Helicopter’s latest Safety Notices.

In May 2013, Robinson Helicopter issued Safety Notice SN-42, Unanticipated Yaw. It said, in part:

A pilot’s failure to apply proper pedal inputs in response to strong or gusty winds during hover or low-speed flight may result in an unanticipated yaw. Some pilots mistakenly attribute this yaw to loss of tail rotor effectiveness (LTE), implying that the tail rotor stalled or was unable to provide adequate thrust. Tail rotors on Robinson helicopters are designed to have more authority than many other helicopters and are unlikely to experience LTE.

I discuss LTE a bit in my 2009 blog post, “How Much Wind is Too Much Wind?” You can also learn about it on Wikipedia and in the FAA-published Helicopter Flying Handbook.

Bell 206 Tail Rotor
Bell 206 helicopters have dinky tail rotor blades. (Photo Credit: Dakota Air Parts.)

Robinson points out that its helicopters are designed to have more authority than many other helicopters. This is partly because Frank Robinson worked for Bell, which has notoriously poor tail rotor authority, where he became known as a “tail rotor expert.”

I experienced the difference between tail rotor authority in a Robinson vs. another helicopter firsthand in 2004, when I flew Bell 206 Long Rangers at the Grand Canyon. After years and at least 1200 hours experience flying Robinsons, I was in a quartering tailwind at the Papillon helipads one day and got into LTE. I pressed the pedal enough to stop the rotation in a Robinson, but the yaw didn’t stop — I wasn’t flying a Robinson. Fortunately, I had the presence of mind to press harder on the pedal and get the situation under control before the rotation had reached a full 90°. It taught me a very valuable lesson about unanticipated yaw.

Robinson’s Safety Notices are normally issued in response to specific accidents. I went fishing on the NTSB website and discovered this April 2012 accident. Probable cause was issued on May 23, 2013 and that would be the right timing for a Safety Notice to appear. (Of course, I can’t be certain whether this is the accident that sparked the new Safety Notice. It’s just a guess on my part.)

From the report summary:

The helicopter slowed as it approached the landing zone on a modified right-base turn to the north. Gusting wind from the south had prevailed for most of the day and was present at the time of the accident. As the pilot turned to “enter the landing area,” he felt a “bump” in the tail rotor control pedals. The pilot added that he applied left pedal to compensate for a right yaw, and the helicopter immediately “started to rotate” at an increasing yaw rate with full left pedal applied. The pilot stated that the rotation stopped when he pushed the collective control “full down” and applied aft cyclic. The helicopter then descended through the trees and collided with terrain. Examination of the wreckage revealed no evidence of pre-impact mechanical anomaly.

The accident report goes on to provide general information about LTE. The Full Narrative refers to FAA Advisory Circular (AC) 90-95 “Unanticipated Right Yaw in Helicopters.” It also refers to Robinson Safety Notice SN-34, Photo Flights – Very High Risk as it pertains to settling with power, reduced RPM, and the loss of tail rotor thrust in low RPM situations. All of this is good reading to learn more about LTE and tail rotor operation.

It’s in low-speed situations that tail rotor effectiveness can be lost. At higher speeds, the helicopter points into the wind via normal “weathervaning.” The vertical stabilizer on the end of the tail helps make this happen. But at lower speeds, especially when turning into a tailwind, the force of the wind can easily cause the helicopter to yaw. The pilot must react quickly and firmly to stop and correct the yaw.

Experience teaches us. Years ago, I was doing a long cross-country flight with a 300-hour pilot who had just gotten his CFI. He was landing at San Luis Obispo (SBP), sitting in the left seat while I sat in the right. There was some yaw and I think he tried to correct it with the pedals. But then he panicked and said that something was wrong, that the pedals weren’t working.

I don’t recall the yaw being very bad. We were still moving along at a good clip, barely over the runway and likely doing at least 50-60 knots. I told him to push the pedal and he claimed he was and that it wasn’t working. He was visibly upset. I offered to take the controls and he agreed. I pushed the appropriate pedal and the helicopter immediately straightened. I landed without incident.

When I read this Safety Notice, I immediately thought of that low time pilot’s approach to landing and my own experience, years before, at the Grand Canyon. In both cases, we’d initially failed to use enough pedal to correct the yaw. The difference is, while I’d added more pedal when necessary, the low-time pilot had assumed there was a problem with the aircraft without trying harder to correct the yaw.

I have to wonder whether the accident pilot was in the same situation. After all, probable cause put the blame firmly on him:

The pilot’s inadequate compensation for wind during a high-power, low-speed downwind turn, which resulted in a loss of control due to loss of tail rotor effectiveness and settling with power. Contributing to the accident was the pilot’s decision to land downwind.

I guess the takeaway from all this can be summed up as follows: We always need to be aware of potential control issues, especially when operating at low speeds in crosswind or downwind situations. Yaw should never be “unanticipated.” It’s the pilot’s responsibility to keep control of the aircraft at all times by avoiding situations that could result in control issues and to use aircraft controls properly.

Airport Tower Closures: Reality Check

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March 24, 2013, 11:30 AM Edit: Got the airplane terminology wrong. Thanks to two airplane pilots for correcting me. I’ve edited the text to show the change. Sorry about the confusion. – ML
March 25, 2013, 2:15 AM Edit: Left out the word towers in a sentence.

Come on folks — it’s not as bad as you think.

Falcon Tower
The control tower at Falcon Field Airport in Mesa, AZ is a typical Class Delta airport tower. (This is not one of the towers scheduled for closure.)

I’ve been reading a lot lately about the FAA’s upcoming airport tower closures. A list is out and there are 149 airports on it. The reduction of funding due to the sequester is making it necessary to close these contracted airport towers all over the country.

Most news articles, tweets, and Facebook updates that I’ve read about the closures are full of doom and gloom. Apparently, a lot of people believe that airport towers are required for safety. But as most general aviation pilots can attest, low traffic airports do not need towers.

What an ATC Tower Does

Air Traffic Control (ATC) towers are responsible for ensuring safe and orderly arrivals and departures of aircraft at an airport. Here’s how it works at a typical Class Delta airport — the kind of airports affected by the tower closures.

Most towered airports have a recording called an Automated Terminal Information System (ATIS) that broadcasts airport information such as weather conditions, runway in use, and any special notices (referred to as Notices to Airmen or NOTAMs). Pilots listen to this recording on a special airport frequency as they approach the airport so they’re already briefed on the most important information they’ll need for landing. The ATIS recording is usually updated hourly, about 5 to 10 minutes before the hour. Each new recording is identified with a letter from the ICAO Spelling Alphabet, or the Pilot’s Alphabet, as I refer to it in this blog post.

Before a pilot reaches the airport’s controlled airspace — usually within 4 to 6 miles of the airport — she calls the tower on the tower frequency. She provides the airport controller with several pieces of information: Aircraft identifier, aircraft location, aircraft intentions, acknowledgement that pilot has heard ATIS recording. A typical radio call from me to the tower at Falcon Field, where I flew just the other day, might sound something like this:

Falcon Tower, Helicopter Six-Three-Zero-Mike-Lima is eight miles north, request landing helipads with Kilo.

An airplane calling in might say something like:

Falcon Tower, Cessna One-Two-Three-Alpha-Bravo is ten miles east, request touch-and-go with Kilo.

Kilo, in both cases, is the identifier of the current ATIS recording.

The tower controller would respond to my call with something like:

Helicopter Six-Three-Zero-Mike-Lima, Falcon Tower, proceed inbound. Report 1 mile north for midfield crossing at nineteen hundred feet.

To the airplane, he might say something like:

Cessna One-Two-Three-Alpha-Bravo, Falcon Tower, enter right downwind for runway four right.

(If you want to see what these instructions mean by looking at a detailed airport diagram, here’s one for you.)

Of course, if the tower controllers were really busy or there was some sort of problem at the airport, the controller could say something like:

Aircraft calling Falcon Tower, remain clear of the class delta airspace.

That means the pilot can’t come into the airspace — which is marked on charts and many GPS models — until the tower clears her in. That happens very seldom.

This is the beginning of the conversation between the air traffic controller in the airport’s tower and the pilot. What follows is a dialog with the tower providing instructions and the pilot acknowledging those instructions and then following them. The controller’s job is to sequence airplane traffic on the airport’s runway(s), making sure there’s enough spacing between them for the various types of landings: touch-and-go, full stop, low approach, etc. In the case of helicopters — which is admittedly what I know best — the tower can either put us into the traffic pattern with the airplanes (which really isn’t a good idea) or keep us out of the airplane flow. The tower clears airplanes to land on the runway and gives permission to helicopters to land in “non-movement” areas.

At the same time all this is going on, the tower’s ground controller is providing instructions to airplanes that are taxiing around the airport, either to or from the runways. Aircraft are given taxi instructions that are sort of like driving directions. Because helicopters seldom talk to towers, I can’t give a perfect example, but instructions from the transient parking area to runway 4R might sound something like this:

Cessna One-Two-Three-Alpha-Romeo, Falcon Ground, taxi to runway four right via Delta. Position and hold Line up and wait at Delta One.

These instructions can get quite complex at some large airports with multiple runways and taxiways.

Position and hold Line up and wait — formerly hold short position and hold — means to move to the indicated position and do not cross the hold line painted on the tarmac. This keeps the airplane off the runway until cleared to take off.

A pilot who is holding short waiting switches to the tower frequency and, when he’s the first plane at the hold line, calls the tower to identify himself. The tower then clears him to get on the runway and depart in the direction he’s already told the ground controller that he wants to go.

Air traffic control for an airport also clears pilots that simply want to fly through the airspace. For example, if I want to fly from Wickenburg to Scottsdale, the most direct route takes me through Deer Valley’s airspace. I’d have to get clearance from the Deer Valley Tower to do so; I’d then be required to follow the tower’s instructions until the controller cut me loose, usually with the phrase “Frequency change approved.” I could then contact Scottsdale’s tower so I could enter that airspace and get permission to land.

A few things to note here:

  • Not all towers have access to radar services. That means they must make visual contact with all aircraft under their control. Even when radar is available, tower controllers make visual contact when aircraft are within their airspace.
  • If radar services are available, tower controllers can ask pilots to Ident. This means pushing a button on the aircraft’s transponder that makes the aircraft’s signal brighter on the radar screen, thus making it easier for the controller to distinguish from other aircraft in crowded airspace. The tower can also ask the pilot to squawk a certain number — this is a 4-digit code temporarily assigned to that aircraft on the radar screen.
  • Some towers have two tower controller frequencies, thus separating the airspace into two separately controlled areas. For example, Deer Valley Airport (DVT) has a north and south tower controller, each contacted on a different frequency. When I fly from the north over the top of the runways to land at the helipads on the south side, I’m told to change frequency from the north controller to the south controller.
  • The tower and ground controllers coordinate with each other, handing off aircraft as necessary.
  • The tower controllers also coordinate with controllers at other nearby airports and with “center” airports. For example, when I fly from Phoenix Gateway (IWA) to Chandler (CHD), the Chandler controller knows I’m coming because the Gateway controller has told him. Similarly, if a corporate jet departs Scottsdale (SDL) on an Instrument Flight Rules (IFR) flight plan, the Scottsdale controller obtains a clearance for that jet from Phoenix Departure or Albuquerque Center.

I should also point out two things from the point of view of a pilot:

  • Dealing with air traffic control does add a tiny bit to the pilot’s workload. The pilot must communicate with the tower before entering the airspace, the pilot must follow the tower’s instructions (unless following those instructions is not safe, of course). I know plenty of pilots who would rather fly around a towered airport’s airspace than fly through it — just because they don’t want to talk to a controller. I’ll admit that I’ve done this quite a few times — I even have a winding route through the Phoenix area between Wickenburg and Chandler that avoids all towered airspace along the way.
  • Air traffic control gives many pilots the impression that they are no longer responsible for seeing and avoiding other aircraft. After all, the tower sees all and guides aircraft to avoid each other. But there have been instances where air traffic control has dropped the ball — I experienced one myself years ago — and sometimes this can have tragic consequences.

Low Traffic Airports Don’t Need Towers

As you can probably imagine, the more air traffic coming and going in an airport’s airspace, the busier air traffic controllers are.

A very busy airport like Deer Valley, which has at least two flight schools, several helicopter bases (police and medevac), at least one charter operator, and a bit of traffic from corporate jets, can keep controllers pretty busy. In fact, one of the challenges of flying in and out of Deer Valley is being able to get a call in on the radio — it’s often a steady stream of pilot/controller communication. Indeed, Deer Valley airport was the 25th busiest airport in the country based on aircraft movements in 2010.

Likewise, at an airport that gets very little traffic, the tower staff doesn’t have much to do. And when you consider that there has to be at least two controllers on duty at all times — so one can relieve the other — that’s at least two people getting paid without a lot of work to do.

Although I don’t know every towered airport on the list, the ones I do know don’t get very much traffic at all.

For example, they’re closing four in Arizona:

  • Laughlin/Bullhead City International (IFP) gets very little traffic. It sits across the river from Laughlin, NV in one of the windiest locations I’ve ever flown into. Every time I fly into Laughlin, there’s only one or two pilots in the area — including me.
  • Glendale Municipal (GEU) should get a lot of traffic, but it doesn’t.
  • Phoenix Goodyear (GYR) is home of the Lufthansa training organization and a bunch of mothballed airliners, but it doesn’t get much traffic. Lufthansa pilots in training use other area airports, including Wickenburg, Buckeye, Gila Bend, Lake Havasu City, and Needles — ironically, none of those have a tower.
  • Ryan Field (in Tucson; RYN) is the only one of the three I haven’t flown into, so I can’t comment its traffic. But given the other airports on this list, I have to assume the traffic volume is low.

They’re also closing Southern California Logistics (VCV) in Victorville, CA. I’ve flown over that airport many times and have landed there once. Not much going on. It’s a last stop for many decommissioned airliners; there’s a 747 “chop shop” on the field.

They’re closing Northeast Florida Regional (SGJ) in St. Augustine, FL. That’s the little airport closest to where my mom lives. When she first moved there about 15 years ago, it didn’t even have a tower.

These are just the airports I know. Not very busy. I know plenty of non-towered airports that get more traffic than these.

How Airports without Towers Work

If an airport doesn’t have a tower — and at least 80% of the public airports in the United States don’t have towers — things work a little differently. Without a controller to direct them, pilots are responsible for using the airport in accordance with standard traffic patterns and right-of-way rules they are taught in training.

Some airports have Automated Weather Observation Systems (AWOS) or Automated Surface Observation Systems (ASOS) that broadcast current weather information on a certain frequency. Pilots can tune in to see what the wind, altimeter setting, and NOTAMs are for the airport.

When a pilot gets close to a non-towered airport, she should (but is not required to) make a position report that includes her location and intentions. For example, I might say:

Wickenburg Traffic, helicopter Six-Three-Zero-Mike-Lima is ten miles north, landing Wickenburg.

An airplane pilot might say:

Wickenburg Traffic, Cessna One-Two-Three-Alpha-Bravo is eight miles southeast. We’ll be crossing midfield at five thousand to enter right traffic for Runway Two-Three.

Other pilots in the area would hear that call and respond by making a similar position call. The calls continue as needed at the pilot’s discretion — the more aircraft in the area, the more calls I make just to make sure everyone else knows I’m out there and where I am. Pilots then see and avoid other traffic to land or depart the airport.

It sounds crazy, but it works — remarkably well. In Wickenburg, for example — an airport that gets a lot of pilots in training practicing takeoffs and landings — there might be two or three or even more airplanes in the traffic pattern around the airport, safely landing and departing in an organized manner. No controller.

And this is going on at small general aviation airports all over the country every single day.

What’s even more surprising to many people is that some regional airlines also land at non-towered airports. For example, Horizon operates flights between Seattle and Wenatchee, WA; Wenatchee is non-towered. Great Lakes operates between Phoenix or Denver and Page, AZ; Page is non-towered.

The Reality

My point is this: people unfamiliar with aviation think that a control tower is vital to safe airport operations. In reality, it’s not. Many, many aircraft operate safely at non-towered airports every day.

While the guidance of a tower controller can increase safety by providing instructions that manage air traffic flow, that guidance isn’t needed at all airports. It’s the busy airports — the ones with hundreds of operations every single day — that can truly benefit from air traffic control.

The 149 airport towers on the chopping block this year were apparently judged to be not busy enough.

I guess time will tell. And I’m certain of one thing: if there is any accident at one of these 149 airports after the tower is shut down, we’ll hear about it all over the news.

In the meantime, I’d love to get some feedback from pilots about this. Share your thoughts in the comments from this post.

The Rules about Flying over Wilderness Areas

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My answer to a reader’s question.

ChartA week or two ago, I got an email message from a reader who had read my November 2011 post, “A Few Aerial Views from Today’s Flight.” That post shows off a bunch of photos captured by my helicopter’s “nose cam,” a GoPro Hero2 camera I sometimes use in flight. The photos include views of the Verde and Salt Rivers north and east of Phoenix, including some of the lakes along the rivers. My reader noticed, after consulting some aeronautical charts, that much of the area I’d flown over was designated as wilderness area.

This reader, who asked to remain anonymous and not be quoted verbatim, was wondering about “bending” rules. Although he mentioned the June 2012 wire strike helicopter crash in the Verde River area, he wasn’t interested in the safety aspects of maintaining a high enough altitude to clear obstacles. He was interested in my interpretation of the rule about flying at least 2,000 feet above wilderness areas.

The “Rule”

Before I interpret the rule, it’s a good idea to know exactly what the rule is and where it can be found.

It’s interesting to note that a search for “wilderness” and “2,000 feet” in the Federal Aviation Regulations (FARs) does not provide any guidance related to operations over charted wilderness areas. The FARs are the rules pilots are required to comply with.

A search of the Aeronautics Information Manual (AIM) for “wilderness” results in “Part 7-4-6: Flights Over Charted U.S. Wildlife Refuges, Parks, and Forest Service Areas.” Paragraph b pertains to this topic:

b. Pilots are requested to maintain a minimum altitude of 2,000 feet above the surface of the following: National Parks, Monuments, Seashores, Lakeshores, Recreation Areas and Scenic Riverways administered by the National Park Service, National Wildlife Refuges, Big Game Refuges, Game Ranges and Wildlife Ranges administered by the U.S. Fish and Wildlife Service, and Wilderness and Primitive areas administered by the U.S. Forest Service.

A note adds this:

FAA Advisory Circular AC 91-36, Visual Flight Rules (VFR) Flight Over Noise-Sensitive Areas, defines the surface of a national park area (including parks, forests, primitive areas, wilderness areas, recreational areas, national seashores, national monuments, national lakeshores, and national wildlife refuge and range areas) as: the highest terrain within 2,000 feet laterally of the route of flight, or the upper-most rim of a canyon or valley.

First Glance Interpretation

At first glance, the “rule” seems pretty straightforward: you’re supposed to fly at least 2,000 feet above the ground in any charted wilderness area, etc.

User's Guide ImageCharts, by the way, make it very easy to identify these areas. They’re normally surrounded by a blue line that has dots on the inside of the area. This entry from the Aeronautical Chart User’s Guide shows what to look for. And this chart excerpt from the Phoenix terminal area chart (TAC) illustrates how two areas look on an actual chart: The Hells Canyon Wilderness area (left) and Lake Pleasant Bald Eagle Breeding Area (right):

Wilderness Examples

The Advisory Circular note goes a bit further to explain that the lowest point in the wilderness area that you should consider when setting your altitude is the highest point 2,000 feet from your aircraft in any direction. So if you’re flying over a 1,000 foot deep canyon and the canyon is only 1,500 feet wide, you should be 2,000 feet above the canyon walls — not 2,000 feet over the bottom of the canyon.

It’s important to note that a requirement like this is extremely difficult for helicopter pilots to deal with, primarily because helicopters normally operate 500 to 1,000 feet above the ground. We seldom fly 2,000 feet above anything — that’s nosebleed territory for us. That’s also where small planes might be operating — and we’re trained to stay away from them. So when you ask a helicopter pilot to fly 2,000 feet above the ground, we’re not going to like it.

But Is It A Rule?

But the real question should be, is this really a rule? Something that must be followed? Something that could get you in trouble with the FAA if you ignore it?

I can offer two arguments for why pilots are not required to fly 2,000 feet above charted wilderness areas:

  • The “rule” is not included in the FARs, which are the regulations governing flight in the U.S. Instead, it’s described in the AIM, which is informational in nature.
  • The language of the “rule” says that “Pilots are requested to maintain a minimum altitude of 2,000 feet above the surface…” Surely you can’t confuse a “request” with a “requirement.”

Before I go any further, I want to point out paragraph c of the same AIM part (7-4-6):

Federal statues prohibit certain types of flight activity and/or provide altitude restrictions over designated U.S. Wildlife Refuges, Parks, and Forest Service Areas. These designated areas, for example: Boundary Waters Canoe Wilderness Areas, Minnesota; Haleakala National Park, Hawaii; Yosemite National Park, California; and Grand Canyon National Park, Arizona, are charted on Sectional Charts.

Note the use of the word “prohibit” in this paragraph. With a little bit of effort, you can find the rules for these areas in the FARs or Special Federal Aviation Regulations (SFARs). For example, FAR 93 Subpart U and SFAR 50-2 govern special regulations over Grand Canyon National Park. In the case of Yosemite the rule is printed right on the chart:

Yosemite on Chart

In case you can’t read it:

Public Law 100-91 prohibits flight of VFR helicopters or fixed-wing aircraft below 2000 feet above the surface of Yosemite National Park. “Surface” refers to the highest terrain within the park within 2000 feet laterally of the route of flight or within the uppermost rim of the Yosemite Valley.

Pretty clear, no?

My point is, don’t get the idea that a pilot can ignore charted wilderness areas. That simply isn’t true. You need to know whether an area has its own special flight regulations before even considering “breaking” the 2,000-foot “rule.”

What’s Right?

Now you know my interpretation. But I didn’t get this on my own. It was pointed out to me by my primary flight instructor years ago. Pilots who take the time to look up and read the “rules” can make their own conclusions.

The reader who queried me about this obviously realized from the photos I shared on my blog post that I must have been flying lower than 2,000 feet above the ground in a charted wilderness area. Denying I did so when there’s photographic evidence to the contrary would be dishonest, insulting to my readers, and a waste of time.

But is it right to fly low over these areas? Because it’s not a regulation in most wilderness areas, it becomes an ethical decision on the part of the pilot.

First, consider why charted wilderness areas exist. The government is protecting these areas, for whatever reason. Usually, it’s because they don’t want aircraft noise to interfere with wildlife — especially wildlife breeding and habitat maintenance. Sometimes its because they want “natural” areas to be kept quiet for visitors trying to enjoy the beauty of nature in peace.

How do you feel about preserving quiet in these areas? Is it important to you? If you were on the ground, how would you feel if a helicopter or plane buzzed by at 500 or 1,000 feet? Would it bother you? How do you think it affects the people on the ground? People camping, fishing, hiking, meditating?

As the person who contacted me pointed out, when he flew in the area, he didn’t see a person for miles. So who would he be bothering?

The one thing I can say with certainty is this: If pilots typically “busted a wilderness area” by flying low through it and enough people on the ground noticed and complained about it, it’s far more likely that the government will respond by establishing a real rule to prevent it. Yes, at one time people were allowed to fly low-level through the Grand Canyon and Yosemite valley. But when enough complaints came in, regulations were written to make such activity illegal.

Would you want to see that happen with all the wilderness areas on the charts?

I know I wouldn’t.