this system, controllers are alerted of wind discrepancies  (an indicator of wind shear possibility) and provide this  information to pilots. A typical wind shear alert issued to a  pilot would be: “Runway 27 arrival, wind shear alert, 20 knot loss 3  mile final, threshold wind 200 at 15” In plain language, the controller is advising aircraft arriving  on runway 27 that at about 3 miles out they can expect a  wind shear condition that will decrease their airspeed by 20  knots and possibly encounter turbulence. Additionally, the  airport surface winds for landing runway 27 are reported as  200° at 15 knots. Pilots encountering wind shear are encouraged to pass along  pilot reports. Refer to AIM for additional information on  wind shear PIREPs. Pilots on IFR flight plans operating in VFR weather  conditions may request VFR-on-top in lieu of an assigned  altitude. This permits them to select an altitude or flight level  of their choice (subject to any ATC restrictions). Pilots desiring to climb through a cloud, haze, smoke, or  other meteorological formation and then either cancel their  IFR flight plan or operate VFR-on-top may request a climb  to VFR-on-top. The ATC authorization contains a top report  (or a statement that no top report is available) and a request  to report upon reaching VFR-on-top. Additionally, the ATC  authorization may contain a clearance limit, routing, and  an alternative clearance if VFR-on-top is not reached by a  specified altitude. A pilot on an IFR flight plan, operating in VFR conditions,  may request to climb/descend in VFR conditions. When  operating in VFR conditions with an ATC authorization to  “maintain VFR-on-top/maintain VFR conditions,” pilots on  IFR flight plans must: Pilots operating on a VFR-on-top clearance should advise  ATC before any altitude change to ensure the exchange of  accurate traffic information. The success of the flight depends largely upon the  thoroughness of the preflight planning. The evening before  the flight, pay close attention to the weather forecast and  begin planning the flight. To illustrate some of the concepts introduced in this chapter,  follow along on a typical IFR flight from the Birmingham  International Airport (BHM), Birmingham, Alabama to  Gulfport-Biloxi International Airport (GPT), Gulfport,  Mississippi.  [Figure 10-18]  For this trip, a Cessna 182 with  a call sign of N1230A is flown. The aircraft is equipped with  dual navigation and communication radios, a transponder,  and a GPS system approved for IFR en route, terminal, and  approach operations. VFR over-the-top must not be confused with VFR-on- top. VFR-on-top is an IFR clearance that allows the pilot  to fly VFR altitudes. VFR over-the-top is strictly a VFR  operation in which the pilot maintains VFR cloud clearance  requirements while operating on top of an undercast layer.  This situation might occur when the departure airport and the  destination airport are reporting clear conditions, but a low  overcast layer is present in between. The pilot could conduct  a VFR departure, fly over the top of the undercast in VFR  conditions, then complete a VFR descent and landing at the  destination. VFR cloud clearance requirements would be  maintained at all times, and an IFR clearance would not be  required for any part of the flight. This clearance must be requested by the pilot on an IFR flight  plan. VFR-on-top is not permitted in certain areas, such as  Class A airspace. Consequently, IFR flights operating VFR- on-top must avoid such airspace. Pilots operating VFR-on-top/VFR conditions may receive  traffic information from ATC on other pertinent IFR or  VFR aircraft. However, when operating in VFR weather  conditions, it is the pilot’s responsibility to be vigilant to see  and avoid other aircraft. ATC authorization to “maintain VFR-on-top” is not intended  to restrict pilots to operating only above an obscuring  meteorological formation (layer). Rather, it permits operation  above, below, between layers, or in areas where there is no  meteorological obstruction. It is imperative pilots understand,  however, that clearance to operate “VFR-on-top/VFR  conditions” does not imply cancellation of the IFR flight plan. VFR-On-Top VFR Over-The-Top Conducting an IFR Flight Preflight 1.  Fly at the appropriate VFR altitude as prescribed in  14 CFR part 91. 2.  Comply with the VFR visibility and distance-from- cloud criteria in 14 CFR part 91. 3.  ComplywithIFRapplicabletothisflight(minimumIFR  altitudes, position reporting, radio communications,  course to be flown, adherence to ATC clearance, etc.). 10-26