-T / T / +T | Comment(s)

Tuesday, November 1, 2005

Tech Talk

Shawn Coyle

Real, Complete Definition of VFR
ONE PROBLEM WITH DISCUSSING this subject is the FAA definition of VFR; it only talks of visibility and distance from clouds. This definition is sadly lacking. Let's look at what must lie behind a complete definition of visual flight rules.

A good place to start is the airworthiness certification requirements for helicopters. The main portions of FAR Parts 27 and 29 are set up for only day and night VFR certification. If you want to certify a helicopter for IFR, there are appendices that dictate equipment and handling needed. All that's needed for VFR certification is an airspeed indicator, altimeter and wet compass. What's interesting is what is missing--an attitude indicator, turn needle or even slip ball.

Yep, you read that right. There is no airworthiness requirement for an attitude indicator to certify a helicopter for day and night VFR. Requirements for commercial operations in many countries include attitude indicators. But per airworthiness rules, you could fly a helicopter at night in a private operation without an attitude indicator. Same thing for nav equipment--airworthiness rules only require a wet compass.

The Implication
From this, we can imply that someone assumed that a pilot flying VFR can determine his helicopter's attitude and navigate by looking outside. Navigation includes determining height above ground, as it's hard to navigate when you're on (or in) the ground, and certainly needs more than a wet compass. You can't correct heading without knowing where you are with respect to a planned course.

We can put the navigation issue to rest. GPS has solved that problem. But we're left with the requirement, unstated by the FAA, to orient the helicopter in attitude and height above ground with visual references.

Let's look at a couple of examples of where the FAA definition falls apart unless you understand the underlying (and unstated) assumptions.

You're cruising along at 500 ft. agl and have to cross a lake 20 mi. across in your minimally equipped helicopter (airspeed indicator, wet compass, altimeter, hand-held GPS). You've determined you have an average of 5 mi. of visibility at the lake's shore. While it's murky, the only clouds are a high overcast layer that might worry only jets. It's a flat, calm day--not a breath of wind. Great VFR weather--right?

Now you're over the middle of the lake--no shoreline to be seen, no waves, no shadows. This is called the fishbowl effect. You think you're inside a fishbowl. Navigation is not a problem; you have GPS. But I defy you to fly safely across this lake without some adventure you might not wish to repeat.

Instrument flying is quite an adventure with only an airspeed indicator, wet compass (down by your right foot) and altimeter (you do have the correct altimeter setting, don't you?). Pitch control isn't much of a problem as airspeed and altitude correlate. Roll control and heading become quite a handful with no discernable horizon. One manufacturer even states, "Lose sight of the horizon and you die."

You can repeat the scenario in a variety of ways--snow-covered lake with overcast sky, night over the middle of the desert with no lights. I'm sure you get the picture.

Now, what if visibility starts to decrease as you cross the lake? Would you know it was getting worse? With no visual references, you can't know what the visibility was. You might not even be legal from the visibility point of view. You can't know.

You could make a case that, even with great visibility and a clearly defined horizon, with no other references (such as over the middle of the ocean) you can't tell height agl., or heading without a compass.

I hope you agree there's a lot more to VFR than just visibility and distance from clouds. A horizon is needed, as are other references.

So what about at night? Over a city or town, it's pretty easy to orient a helicopter. The lights below make visibility and height above the ground easy to judge.

'Contact Flight'
Go a short distance away, over water or a large expense of forest or desert, with no lights, a high overcast and no moon, and all the visibility and cloud clearance in the world won't help you. You have no way to orient your helicopter without reference to instruments.

Countries other than the United States have more complete VFR definitions that include the requirement to orient by reference to the ground. Most European countries don't have night VFR. Night flying is IFR, with appropriate rules and equipment requirements. Long ago, U.S. regulations contained something called "contact flight," which was defined as flight "in which the attitude of the aircraft and its flight path can at all times be controlled by means of visual reference to the ground or water." I wonder why this very useful definition went away.

The accident rate for helicopters (and light fixed-wing) at night and in less than ideal visual conditions shows that the real and complete definition of VFR isn't well understood. Given the FAA's definition, this is perhaps not surprising.

Shawn Coyle is the chief of flight operations for Agusta Aerospace Corp. He has more than 25 years in helicopter flight testing, including stints as an instructor at the U.S. Naval Test Pilot School, and has flown more than 40 different helicopter types. You can reach him at rotorandwing@accessintel.com.

Live chat by BoldChat