Helicopter Flight Information
|
Helicopter Flight Information |
|
|
HELICOPTER AIRPORT and TRAFFIC PATTERN PROCEDURES
In order to understand helicopter airport operations it is first necessary to understand the procedures for airplanes and the general rules requiring that helicopters avoid the normal flow of fixed wing traffic as stated in the federal aviation regulations FAR § 91.126 (b)(2). The general rule for fixed wing traffic patterns at uncontrolled airports is: Piston engine airplanes should fly a pattern remaining within approximately ½ mile of the runway at a pattern altitude of 1000 feet above field elevation. Turbine fixed wing traffic should fly a pattern altitude of 1500 feet above field elevation, and they will remain within approximately 1-mile of the runway. With consideration to the above-mentioned rule, helicopters should fly a traffic pattern opposite that of fixed wing aircraft and at a traffic pattern altitude of 500 feet above field elevation remaining within approximately ¼ mile of the runway. These distances from the runway will vary per the aircraft (see FAA advisory circular). It is often thought that the pattern altitude at uncontrolled airports for piston airplanes is 800 feet above field elevation, which it once was. The FAA changed their stand on this issue and released Advisory Circular AC 90-66A pertaining to it. The preferred altitude for piston airplanes is now 1000 feet above field elevation unless stated otherwise in the AF/D. This makes sense because the extra 200 feet is necessary for clearance of helicopters and for the general safety of flight. Unfortunately many airports are still listed in the AF/D as 800 feet above field elevation even with the change from the FAA and the increased safety of a higher altitude. There is a reason for the altitude and distance from the airport that these aircraft fly, and with a little thought it makes sense. When aircraft are flown in these patterns they will likely be within gliding distance of the runway or at least reasonably close. A helicopter has a gliding profile slightly better than a brick, so if you are within ¼ mile of the runway at 500 feet AGL you probably can make the runway should your engine fail. Actually a helicopter with a sink rate of 1500 feet per minute at 60 MPH will glide 1380 feet from 500 feet AGL; just slightly greater than ¼ mile. Consider a piston fixed wing aircraft with a sink rate of 600 feet per minute flying ½ mile from the runway when the engine fails. With the proper glide configuration established the aircraft will glide approximately 5760 feet. Keep in mind that these glide times are from the pattern altitude until the wheels contact the runway. A piston fixed wing aircraft should generally turn to the crosswind at about ½ mile beyond the end of the runway at 500 feet AGL remaining within about ½ mile at all times. A helicopter should turn the crosswind and base at or near the abeam point of the ends of the runway, and the downwind should be flown within ¼ mile of the runway centerline. If airplanes are flying a standard left hand traffic pattern, then helicopters should fly a right hand traffic pattern and vice-versa when logically possible (see figure 4). Proper pattern entry procedures are as follows; the standard entry to the traffic pattern should be flown at the traffic pattern altitude from two-miles out on a forty-five degree entry to the mid-field down-wind of the runway in use. If you are approaching from the opposite side of the pattern and if traffic is light and there is no unusual activity going on, over fly the center of the field at traffic pattern altitude for a mid-field down-wind entry to the pattern. The preferred entry from an opposite pattern approach would be to over fly the field at least 500 feet above the traffic pattern altitude continuing outbound for two miles and then turning a descending teardrop back to the more appropriate 45-degree pattern entry. It is most important that an aircraft is at pattern altitude 2 miles from the airport to avoid a dangerous descent into the traffic pattern. Sooner or later you will see a pilot flying a Cessna 172 on a 747 flight pattern complaining because someone cut him or her off on final. Although no aircraft should be cut-off when on final there is no reason to follow another aircraft on such a ridiculous flight path when you can make a safe pattern in front of him or her. There are some pilots who will call a long final and although technically an aircraft on final always has right-of-way some of these pilots are taking advantage of this fact to displace other aircraft established in the pattern. Safety of flight is what is important and reasonable separation must be maintained. If it is clearly safe to shorten your approach there is no reason to follow an aircraft that does not fly a reasonable pattern. It is completely inappropriate and rude to call long final approaches. An aircraft is on final approach when within 1-mile of the runway. Prior to that the aircraft is on a straight in approach. Aircraft that are approaching the airport that are not established in the pattern should yield to those who are established in the pattern even if they are intending a straight in approach to the runway in use. At controlled airports, controllers will frequently direct helicopters directly to their destination on the field. Controllers will expect that helicopters approach the field at the proper pattern altitude of 500 feet AGL, and they will be expecting the helicopters to be at this altitude far enough out (2-miles) to avoid conflicts with fixed wing traffic operating at the airport at their respective proper altitudes. At uncontrolled airports helicopters should approach the airport at 500-feet AGL, and to grass areas parallel the runway in use or to taxiways or other areas so as not to interfere with fixed wing aircraft established in the pattern. Helicopters should also avoid over-flying fixed wing aircraft, and people or vehicles on the ground at altitudes of less than 50 feet AGL. It is perfectly fine for helicopters to use runways so long as they do not interfere with fixed wing aircraft in a dangerous way. While hovering a helicopter close to a taxiway where an airplane is approaching you should land the helicopter or move away so the rotor wash does not shake the airplane. When hovering about the surface you should stay at least 3 rotor diameters away from airplanes on the ground and even further from gliders and ultra-lights. The effect that winds have on rotor downwash must not be forgotten or overlooked. The wind causes vortex drift similar to forward flight. You can see this effect if you hover a helicopter near a water puddle or tall grass first downwind and then upwind. It is important that you take these factors into consideration when you are moving about the surface. You must know where your downwash is going to go, and you must adjust your ground movements accordingly (see figure 12). Airplane pilots should have some degree of education about avoiding helicopters but there will be the occasional airplane pilot who will tie down right next to a helicopter and then he or she will have a heart attack when the helicopter departs and the airplane is shaken against the tie downs or blown half way across the field. Never land or depart when you are, or will be closer than 3 rotor diameters from another helicopter when its rotor is less than full rpm. Your wash could cause the low speed rotor to flap and chop the tail boom. Be cautious when landing next to helicopters where the pilots have not tied the rotors; your downwash can cause the rotor to flap violently against its stop. ☺
|
Send email to
rb@helicopterflight.net with
questions or comments about this web site.
|