These words are in the back of any professional pilot’s mind and it certainly applies to TAF constraints. When flying from A to B, an airport C is required as an alternate. Many think pilots fly around with full fuel tanks. Not so. We are obviously given the fuel to fly to the destination airport, shoot the approach, carry out the missed approach (if need be) and fly to the plan B airport and then have only 30 minutes of FIT (Fuel In Tanks) remaining.
For example, when flying to YHZ (Halifax) from YYZ we may use YQM (Moncton) as an alternate. And as one crusty captain said, “I don’t care what the destination weather is doing, I want to know if I have a legal alternate!” So if YQM only has a non-precision approach the limits are 800 and 2. If the ILS (precision approach) is working, the alternate limit lowers to 600 and 2. But there is the sliding scale in Canada. An 800 and 2 limit can slide to 900 and 1 ½ or 1000 and 1. Try deciphering if it is a legal alternate on a 12-hour duty day while flying around in a hold during the wee hours of the night. Then if two precision approaches are available, the alternate limit is 400 and 1, or 200 feet and ½ above the HAT (Height Above Touchdown).
For a pilot…visibility, ceiling and winds are the priority parameters. For me, I believe the TAF format looks after things nicely. Flight dispatchers have possibly 25 flights per shift so they too have to rely heavily on their accuracy. The flight plan software itself decides the take off and landing runway based on TAF winds. Dispatchers must also perform flight following duties to ensure the TAF is holding up.
Many airlines are now allowed to fly to their destination without an alternate. So when a pilot flies from A to B with “no alternate IFR,” enough fuel is boarded for the flight plus 30 minutes of FIT with extra “statistical fuel” compiled from numerous flights. This ‘squirt of statistical fuel’ equates to about 10 minutes. So that crusty captain no longer cares about an alternate, but he sure hopes the destination TAF is spot on. And speaking of limits, the destination airport must be within Canada and the USA, and be within six hours of flight from the departure airport. The weather +/- an hour of the ETA must be forecast 1500 and 6 for Canada and 2000 and 3 for US airports. No mention of freezing precipitation, fog or thunderstorms can be in the TAF plus two separate runways must be available.
Fuel is the number one expense for any airline. The TAF has to be accurate, because fuel is boarded to within the nearest 100 kg. As an ex-MT, I believe Canadian TAFs work very well and I can appreciate the difficulty in forecasting certain weather events. Unfortunately, many pilots think aviation forecasts should be cut and dried. In other words, its accuracy should be within minutes, cloud heights to within feet and visibility within ¼ mile. And some forecasters think they can comply with those constraints.
“Am I legal” is a phrase that bounces around most pilot’s heads. TAFs are part of the legalese and no one ever remembers when the weatherman is right.