Index   268 -- Page 269 -- 270

11/10/16
12/10/15                                                                                                          AIM



     1. Weather Encounters Inducing Altitude                 gained since 1997 has shown that such encounters in
Deviations of Approximately 200 feet. When the               RVSM airspace are generally moderate or less in
pilot experiences weather induced altitude deviations        magnitude.
of approximately 200 feet, the pilot will contact ATC
and state "Unable RVSM Due (state reason)"                     b. Prior to DRVSM implementation, the FAA
(e.g., turbulence, mountain wave). See contingency           established provisions for pilots to report wake
actions in paragraph 4-6-9.                                  turbulence events in RVSM airspace using the NASA
                                                             Aviation Safety Reporting System (ASRS). A
     2. Severe Turbulence (including that associ-            "Safety Reporting" section established on the FAA
ated with MWA). When pilots encounter severe                 RVSM Documentation webpage provides contacts,
turbulence, they should contact ATC and report the           forms, and reporting procedures.
situation. Until the pilot reports clear of severe
turbulence, the controller will apply merging target           c. To date, wake turbulence has not been reported
vectors to one or both passing aircraft to prevent their     as a significant factor in DRVSM operations.
targets from merging:                                        European authorities also found that reports of wake
                                                             turbulence encounters did not increase significantly
EXAMPLE-                                                     after RVSM implementation (eight versus seven
"Yankee 123, FL 310, unable RVSM due severe                  reports in a ten-month period). In addition, they
turbulence."                                                 found that reported wake turbulence was generally
                                                             similar to moderate clear air turbulence.
"Yankee 123, fly heading 290; traffic twelve o'clock,
10 miles, opposite direction; eastbound MD-80 at               d. Pilot Action to Mitigate Wake Turbulence
FL 320" (or the controller may issue a vector to the         Encounters
MD-80 traffic to avoid Yankee 123).
     3. MWA. When pilots encounter MWA, they                    1. Pilots should be alert for wake turbulence
should contact ATC and report the magnitude and              when operating:
location of the wave activity. When a controller                   (a) In the vicinity of aircraft climbing or
makes a merging targets traffic call, the pilot may          descending through their altitude.
request a vector to avoid flying directly over or under
the traffic. In situations where the pilot is                       (b) Approximately 10-30 miles after passing
experiencing altitude deviations of 200 feet or              1,000 feet below opposite-direction traffic.
greater, the pilot will request a vector to avoid traffic.
                                                                    (c) Approximately 10-30 miles behind and
Until the pilot reports clear of MWA, the controller
                                                             1,000 feet below same-direction traffic.
will apply merging target vectors to one or both
passing aircraft to prevent their targets from merging:           2. Pilots encountering or anticipating wake
EXAMPLE-                                                     turbulence in DRVSM airspace have the option of
"Yankee 123, FL 310, unable RVSM due mountain wave."         requesting a vector, FL change, or if capable, a lateral
                                                             offset.
"Yankee 123, fly heading 290; traffic twelve o'clock,
                                                             NOTE-
10 miles, opposite direction; eastbound MD-80 at
                                                             1. Offsets of approximately a wing span upwind generally
FL 320" (or the controller may issue a vector to the
                                                             can move the aircraft out of the immediate vicinity of
MD-80 traffic to avoid Yankee 123).
                                                             another aircraft's wake vortex.
    4. FL Change or Re-route. To leave airspace              2. In domestic U.S. airspace, pilots must request clearance
where MWA or severe turbulence is being                      to fly a lateral offset. Strategic lateral offsets flown in
encountered, the pilot may request a FL change               oceanic airspace do not apply.
and/or re-route, if necessary.

                                                             4-6-8. Pilot/Controller Phraseology
4-6-7. Guidance on Wake Turbulence
                                                             TBL 4-6-1 shows standard phraseology that pilots
  a. Pilots should be aware of the potential for wake        and controllers will use to communicate in DRVSM
turbulence encounters in RVSM airspace. Experience           operations.


Operational Policy/Procedures for Reduced Vertical Separation Minimum (RVSM) in the                              4-6-5
Domestic U.S., Alaska, Offshore Airspace and the San Juan FIR