 U.S. Department of Transportation
Federal Aviation Administration |
CAUTION Wake Turbulence
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Remember, the best defense against wake turbulence is to know and avoid areas where it occurs.
The
intensity or strength of the vortex is primarily a function of aircraft
weight and configuration (flap setting etc.). The strongest vortices
are produced by heavy aircraft, flying slowly, in a clean
configuration. For example, a large or heavy aircraft that must reduce
its speed to 250 knots below 10,000 feet and is flying in a clean
configuration while descending, produces very strong wake. Extra
caution is needed when flying below and behind such aircraft.
Short wing span aircraft are most susceptible to wake turbulence. The wake turbulence-induced roll rates can be extreme. Countering roll rates may be difficult or impossible even in a high performance aircraft with excellent roll control authority.
will tend to keep the upwind vortex in the runway area and may cause the downwind vortex to drift toward another runway.
At altitude, vortices sink at a rate of 300 to 500 feet per minute and stabilize about 500 to 900 feet below the flight level of the generating aircraft.
Helicopters
also produce wake turbulence.
Helicopter wakes may be of significantly greater strength than those
from a fixed wing aircraft of the same weight. The strongest wake can
occur when the helicopter is operating at lower speeds (20 - 50 knots).
Some mid-size or executive class helicopters produce wake as strong as
that of heavier helicopters This is because two blade main rotor
systems, typical of lighter helicopters, produce stronger wake than
rotor systems with more blades.
Use extreme caution to intercept final above or well behind the heavier
aircraft. When a visual approach is issued and accepted to visually
follow a preceding aircraft, the pilot is required to establish a safe
landing interval behind the aircraft s/he was instructed to follow. The
pilot is responsible for wake turbulence separation. Pilots must not
decrease the separation that existed when the visual approach was
issued unless they can remain on or above the flight path of the
preceding aircraft.
If you have recently experienced wake turbulence, tell the Aviation Safe Reporting System (ASRS) about it. The ASRS is one of the ways the industry learns about safety issues. You can also help support an FAA effort to reduce the frequency and danger of wake vortex events.
Report participation is voluntary and all identifying information will be removed before the ASRS research data are given to the FAA. You can report a wake turbulence incident to the ASRS by completing a NASA/ASRS form obtained from your company, a Flight Service Station, or directly from NASA. Write to NASA/ASRS at 625 Ellis Street, Suite 305, Mountain View, California 94043, phone (415) 969-3969 or fax (415) 967-4170.
The people at ASRS may call you and request to interview you about the wake vortex incident. Participation in the callback program is also voluntary, and confidential Your information will help improve the safe of the National Airspace System.
"It felt as though we had hit a twenty-foot thick concrete wall."The above are actual excerpts from reports to the Aviation Safety Report System (ASRS).
Statement from a corporate pilot after hitting the wake
from a large aircraft in a slow descent across his flight path."We were cleared for a visual approach to the right runway and to maintain visual separation on a wide-body cleared to land on the left. Our yaw damper was MEL'ed inoperative and the aircraft kind of wallowed in the landing configuration. At 2,200 feet MSL. on about a 7 mile final, the aircraft began an abrupt roll to the left and the nose pitched down. Full scale deflection of the yoke to the right did not arrest the left roll and for a moment, it appeared the aircraft was going to roll over onto its back. Suddenly, the aircraft began to recover as the ailerons regained effectiveness. The rest of the approach and landing were normal. The winds were from the left and must have caused the wake vortices from the wide-body to drift toward the right runway final."
Statement from pilot flying a regional turboprop."While holding for an IFR release, a large military transport was cleared for a low approach and to remain in the pattern. Approximately 2 to 3 minutes later, I was cleared for takeoff. After takeoff, I cleaned the aircraft up and climbed about 20 knots faster than normal. Going through 1,200 feet MSL, I lowered the nose slightly because I thought I had cleared the crosswind path of the military transport. About that time, the aircraft began a smooth roll to the left and felt like it was trying to pitch up. I applied nose down pressure and then heard the engines cavitate and we pitched down rather abruptly. The aircraft then felt solid, so I throttled back and gradually pulled up and resumed the climb. The incident shook up some of the passengers, so I explained to them what I thought had happened and that I was going to return to the airport. In all my years of flying, this is the first time I have encountered the wake from a large aircraft."
Statement from a light transport pilot.
A self addressed mailing label will speed processing and delivery
A wake turbulence Training Aid has been developed by the FAA and industry. The training aid includes a report, a videotape, and a CD-ROM. Copies of the training aid are available for a fee from:
or call: 703.487.4650. Request the following NTIS Accession Numbers:
Also, there is a section on wake turbulence in the current Aeronautical Information Manual (AIM).
To receive a printed copy of publication No: ASY-20 95/003
"CAUTION Wake Turbulence" brochure from which these pages are based, write:
You may also leave your request with an automated telephone answering service by dialing: (202) 267-7770