Figure 1-33 Differences Between Military and International TAFs

CHAPTER ONE

METEOROLOGY FLIGHT PLANNING

TAF Differences

U.S. Military TAF

International TAF

Forecast Period

24 Hours

Forecast Period

Variable

Wind Speed

Knots

Wind Speed

Knots-, or Meters- or

Kilometers-per-hour

CAVOK not used

CAVOK used

Figure 1-33 Differences Between Military and International TAFs

The term CAVOK is similar to the term sometimes used among aviators, CAVU, which stands

for "Clear Air, Visibility Unlimited." The term CAVOK stands for "Clear Air, Visibility O.K."

and is not used in U.S. Military TAF reporting.

110.

DETERMINATION OF CEILING IN METARS AND TAFS

We first introduced the concept of cloud layers and ceilings. As you may recall, the definition of

a ceiling is the height above the ground (AGL) ascribed to the lowest broken or overcast layer; or

the vertical visibility into an obscuring phenomenon (total obscuration). Remember partial

obscurations, such as FEW000, or SCT000, do not constitute a ceiling.

Ceilings may be easy to determine in METAR, but more difficult in TAFs, since they usually

have more than one line. Therefore, it is important to carefully evaluate the ceiling by using the

appropriate time period, as will be discussed below in "Using TAFs for Flight Planning." Once

the ceiling (and other cloud layers) has been determined, then one can move onward to

determining the type of flight plan (IFR or VFR) as well as whether an alternate landing airfield

is required.

111.

IFR/VFR RULES FOR FLIGHT PLANNING

The governing service instructions mandate VFR flights maintain certain ceiling and visibility

minimums. The Chief of Naval Operations Instruction 3710.7 series, NATOPS General Flight

and Operating Instructions, referred to as OPNAV 3710.7, or as "the 3710", requires VFR flights

to maintain ceiling and visibility minimums of at least 1000 feet and three statute miles. Air

Force Instruction 11-202 (Vol. 3), General Flight Rules, requires VFR flights to maintain ceiling

and visibility minimums of at least 1500 feet and three statute miles. In other words, existing

and forecast weather must be such as to permit VFR operations for the entire duration of the

flight and at the destination, including +1 hour of the ETA (both services). If this cannot be

maintained, as determined by reference to the applicable METAR and TAF products, then one

must file and fly an IFR flight plan.

112. REQUIREMENTS FOR AN ALTERNATE ON IFR FLIGHT PLANS

Each airfield has minimum ceiling requirements for commencing an approach and landing at that

field. These minimums are found on the airfield's approach plates and play an important role in

1-28 AVIATION ROUTINE WEATHER REPORTS AND TERMINAL AERODROME

FORECASTS