Last updated: 09/19/2007
|Chopper 101 -- Infomation to help fixed-wing pilots predict what we'll do next!|
This page is a result of postings on the Pilots of America web board. It is an attempt to explain how we helicopter pilots conduct operations near airports, in the hope that what we do becomes more predictable to fixed-wingers. The inspiration comes from a post by a fixed-winger asking how come we fly opposite traffic from them, for example right turns in a traffic pattern instead of left turns. He felt this was unsafe because, I think, he just didn't understand what we do and why. I will use terminology that pilots use, so this page may not make a lot of sense to non-aviators.
A caution about the FARs
When reading the FARs, particularly part 91, you need to pay attention to whether the term "aircraft" is used or "airplane". "Aircraft" means just that -- all aircraft are affected. "Airplane" means just that too -- a helicopter is not an airplane and is therefore not affected by that provision.
Traffic Pattern, Landing, and Takeoff Operations
91.126 (b)(1) constrains airplanes, but not helicopters, to making left traffic in the absense of visual makers indicating right traffic. 91.126 (b)(2) simply says that helicopters must avoid the flow of fixed-wing aircraft. Let's talk about what that means.
Turns: In the absense of traffic, that means that I, as a helo driver, have the option of making either left or right traffic. Generally I will choose whatever gets me on the ground the easiest. If there's enough traffic that I might screw up the fixed-wing flow, then I will usually fly opposite traffic, that is, make right traffic if the fixed-wings are making left. My practice is to always announce what kind of traffic I am making, e.g. "Podunk traffic, helicopter turning right base runway 10, Podunk". But other pilots may not announce turn direction, so it's important for fixed-wing pilots to make their traffic scan include aircraft flying an opposite pattern!
Pattern size: Helicopters generally fly much tighter patterns than fixed-wing a/c do. A 1/2 mile downwind and a 1/4 mile base are pretty common. Which means that when you're scanning for traffic, we're going to be a whole lot closer than you expect. If there's no traffic, we might even turn base before even being opposite the numbers, especially if our destination is somewhere midfield.
Pattern altitude: The AIM talks about pattern altitudes for airplanes, but not helicopters. I generally enter the pattern at about 500' agl, and maintain that for most, but not necessarily all, of my downwind (if any!). The message here is kind of the same: on downwind and entry to base, we are usually going to be lower than you expect!
Base to final and short final: Here's where things get even more interesting! I can't tell you how many times I've had an airplane pull onto a runway when I'm either in my base to final turn, or am on final. This, in spite of my announcing the turn to final. So how come is that?
I think the reason is that fixed-wingers assume that all aircraft are going to fly along the glideslope. Great for airplanes, not so great an assumption when helos are involved! I can think of only two reasons to make a shallow approach in a helicopter. One is under high density altitude conditions, especially when heavy, when I don't know if I'm going to have enough power to come to a hover. Let's face it -- ya don't want to pull pitch to come to a hover and have the helicopter drop to the tarmac under you! So in high DA, we make shallow approaches with the expectation that we may be making a run-on landing (to the accompaniment of a shower of sparks and some really neat sounds as the skid shoes touch). The other time is when there's a hydraulic failure in a ship with hydraulic controls. The landing is similar -- a running touchdown at 20 kt or so (because the helicopter is very, very difficult to control at lower speeds, and a hover is virtually impossible).
So if neither the high DA or hydraulic failure scenarios apply, we're going come in at a much steeper angle than the glideslope for airplanes. This means that if you are looking for a helicopter that's on final, and you look where you'd expect an airplane, you're going to miss the helo because he is going to be a whole lot higher than you expect. It is not at all unusual, depending on actual landing spot, for us to cross the threshhold at 100-200' and possibly higher than that in a practice autorotation (more about autos later). Click on the thumbnail to see what an actual approach looks like (this one is to the taxiway and the altimeter is showing 200' AGL). Look at the picture closesly, and you'll see why fixed-wing pilots look in the wrong place for helicopters!
Parallel Landings and Takeoffs: These are landings and takeoffs to either a taxiway or grass on one side of a runway (the above picture shows one). The reason may be conflict with fixed-wing traffic, or may just be the pilot's whim! The announcement might go something like: "Podunk traffic, helicopter base to final runway 8, landing parallel to the north of the runway, Podunk".
Freeform landing and takeoffs: Ok, I made up the name. What I mean are landings and takeoffs, usually into the wind, that do not parallel a runway. The why is obvious -- it's always better to takeoff and land directly into the wind, particularly because there are some crosswind issues when the wind is anywhere from the left (for U.S. style helicopters -- some foreign ones are the reverse). It is not unusual at all for a tower to hand you one of these because it keeps you away from the flow of traffic. The announcement could be: "Podunk traffic, helicopter is departing to the north from midfield runway 27 (or taxiway, or whatever), Podunk".
Takeoff Profiles: A helicopter is capable of takeoff profiles which cover the whole range from very shallow to vertical. The two that are probably most commonly used are the "normal" profile and the "max performance" profile.
If there are no obstructions, the normal profile is generally regarded as the safest. It starts from a hover, and the pilot moves the stick forward slightly. As the ship accelerates, the pilot holds the nose down, shooting for something like 50' AGL when it reaches 50 KIAS. After reaching 60-65 KIAS, that airspeed is generally held until desired altitude is reached. This profile resembles a fixed-wing profile.
A max performance takeoff is a bird of a different feather. It too starts from a hover. The pilot raises collective to maximum permitted power, and holds the ship in a level attitude, and manages airspeed to stay at about 40 KIAS until the obstacle is cleared. He then lowers the nose and accelerates to 65-65 KIAS just like in a normal takeoff. This profile is frequently used for "freeform" takeoffs because there are usually obstacles of some kind.
Maneuvers Practiced at Airports
When I was a fixed-wing student, I was totally confused by things that helicopter students were doing! So I'm going to try to shed some light on maneuvers that are practiced during both primary and recurrent training.
Autorotations: An auto is to the helicopter pilot what a dead stick approach is to the airplane. Helicopter rotor systems are driven by a gizmo called a sprag clutch. A sprag clutch is essentially a one way drive coupler -- turned in one direction it transmits torque -- turned in the other direction it freewheels. So long as the engine and transmission are operating, the sprag clutch transmits torque to the rotor system and makes it turn. In the event of an engine or transmission failure, the sprag clutch lets the rotor system freewheel. The air coming up through the main rotor then causes the rotor system to keep turning, and the outer part of the blades produce lift.
A practice auto is normally initiated at around 700' agl. Typically, the pilot will fly a wider pattern with a long final for a straight-in auto, a wide downwind but very short base for a 90 degree auto, or a very tight downwind for a 180 degree auto. In a Robinson, entry is usually around 70-75 KIAS. The 90 and 180 autos differ for a straight-in mostly in the entry point (a 90 is entered from base and has a 90 degree turn to final, a 180 from tight downwind with a 180 degree turn to final).
Entry consists of lowering the collective, using antitorque pedal to keep the ship straight, closing the throttle, and then managing airspeed and rotor RPM with collective and cyclic. In Robinsons we shoot for about 65 KIAS and 100% RPM (there are reasons that we might want to vary from these numbers however). At this point the helicopter is dropping pretty fast, somewhere in the vicinity of 1,500 FPM. We ride it down at our chosen airspeed and RPM. At around 40' in real life, a little higher in practice, the pilot will flare the aircraft to convert airspeed into rotor RPM and to stop the descent. As the pilot completes the flare, he will either cushion the landing using the collective or do a power-on recovery with no touchdown. The helicopter makes a very distinctive sound during an auto -- once you hear one, you'll recognize it easily.
Now why go into all this? Because a practice auto will have the ship coming in very high, and then doing a very steep descent. It will definitely not be where you expect to find it! Occasionally you may see an auto initiated from a hover. The aircraft will be stationary, and probably up around 1,000' AGL before the auto is initiated, and thus, even higher than you might normally expect.
Quick stops: The FAA has some other name for these that I can't remember! A Q-stop is practiced, usually on a runway, taxiway or over grass, by starting from a hover, then accelerating as though taking off. As airspeed builds and the ship starts to climb, the pilot lowers collective and flares with cyclic similar to the flare in an auto. Because this is a power on maneuver, he brings in collective to stop the descent to come to a normal hover. The first time I saw a Q-stop I thought the student had lost control! By the way, if the runway is clear, a pilot might practice 3 or 4 Q-stops in succession, and then departing from the end of the runway. The purpose of practicing these is so that when the fuel truck pulls out in front of you, that have a way of stopping the ship before turning everything into a ball of fire...
Pirouettes: This a real fun manuever, not usually taught to primary students. It's generally performed on a runway to give more space. The idea is to come to a hover over the centerline and at 90 degrees to it (i.e. facing away from the runway). The pilot then uses either right or left cyclic to start the helicopter flying sideways in the desired direction and applies either left or right pedal to initiate a slow spin. The trick is to remain over the centerline with a continuous spin and moving continuously down the runway. It is basically a coordination exercise, but looks truly goofy to the uninitiated!
The "Oh crap, we're not gonna clear the trees" Maneuver: I don't know if this even has a name (if it does, and somebody knows it, please let me know). This is a kind of fun advanced maneuver. It is started as a max performance takeoff where it is impossible to clear the obstacle. At some point, bopping along at 40 KIAS, it becomes clear that you ain't gonna make it. So instead of flying into the trees (or whatever), you bring the stick back to slow the helicopter and start it moving backward. It may be necessary to manage collective so that you have a slow, steady, backwards descent back into where you started. Now, of course, you have to figure out some new takeoff strategy, but at least you haven't crashed the ship!
Other Maneuvers: There's lots of other practice maneuvers done around airports, generally over a grassy area or a helipad. These include various hover maneuvers (including the misnamed "hovering auto", which is not an auto at all), slope landings, run on landings to grass, and numerous others. I don't really want to get in to more detail about these since there are no safety issues to fixed-wingers.