Weather minimums are one of the areas where Canadian regs differ most from the FAA, and the INRAT tests them directly. Takeoff minimums, approach bans, and alternate requirements all have specific numbers you need to know. This covers the ones that actually show up on the exam.
Takeoff minimums
Under CARs, there's no single universal takeoff minimum for IFR. It depends on the aircraft category and what's published for the aerodrome.
For aerodromes with a published aerodrome operating minima (AOM), you must meet those published minimums before departing. For aerodromes without published AOM, Transport Canada expects the PIC to determine that the departure can be made safely — including being able to return to land if something goes wrong after takeoff.
The practical takeoff minimums most INRAT questions reference: RVR 1200 feet for single-runway operations under a standard instrument departure, or 1/4 SM visibility if RVR is not available. Know these numbers.
The approach ban
This is tested heavily. The approach ban rule prevents commercial operators from beginning or continuing an approach below 1,000 feet AGL when the reported weather is below published minimums.
- At or above 1,000 feet AGL — you may commence the approach regardless of reported weather
- Below 1,000 feet AGL — if the latest weather report shows conditions below published minimums, you must execute a missed approach
- The key word is "reported" — you use the most recent report available, whether ATIS, METAR, or a direct tower report
Decision Height and Minimum Descent Altitude
Precision approaches (ILS, LPV) use a Decision Height (DH) — you're descending on the glidepath and you decide at DH. Non-precision approaches (VOR, NDB, RNAV LNAV) use a Minimum Descent Altitude (MDA) — you level off at MDA and fly to the missed approach point.
At DH or MDA, you need specific visual references to continue to land. Under CARs, the required visual references include the approach lights, runway lights, threshold, or markings. "I think I can see something" is not enough — the reference must be one of the listed items and must be identifiable.
Alternate aerodrome weather requirements
You need an alternate on your IFR flight plan when the destination weather is forecast to be below certain thresholds at ETA plus or minus one hour:
| Approach available at destination | Alternate required if forecast below |
|---|---|
| Precision approach (ILS) | Ceiling 1,500 ft / Visibility 3 SM |
| Non-precision approach | Ceiling 2,000 ft / Visibility 3 SM |
| No instrument approach | Alternate always required |
The alternate itself also needs to meet minimum weather requirements at your ETA. For an alternate with a precision approach, the forecast must be at or above 600 feet and 2 SM. For a non-precision alternate, 800 feet and 2 SM.
Cold temperature corrections
Canada's temperature range makes cold temperature altitude corrections an exam topic that American study materials never cover. At very low temperatures, your altimeter reads higher than your actual altitude because cold, dense air compresses the atmosphere. The published approach minimums assume ISA conditions.
Transport Canada publishes a cold temperature correction table in the AIM. The INRAT will give you a temperature and a charted altitude and ask you to calculate the corrected altitude. The corrections are significant — at -50°C and a charted altitude of 1,000 feet, the actual correction can exceed 300 feet.
Learn to read the correction table, not just the concept. The exam uses it.
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