Altimeter regions and settings
Region decides the Kollsman window setting (CAR 602.35-602.37): ASR or SPR. A designated mountainous region is a further division designated to increase safety, or for remote or mountainous regions (TC AIM RAC 2.9).
| Region | Covers | Fly on |
|---|---|---|
| Altimeter setting region (ASR) | Low-level airspace delineated in the Designated Airspace Handbook | Current altimeter setting (not station pressure). En route: nearest station along route (sample Q18 key 1; TC AIM RAC 2.10) |
| Standard pressure region (SPR) | All Canadian airspace outside the ASR (CAR 101.01(1)): high-level, plus low-level outside ASR boundaries (TC AIM RAC 2.11) | 29.92" / 1013.2 mb. Altitude read against it is a flight level (FL), in hundreds of feet (CAR 101.01(1)) |
Each equipped crew position sets:
| Region | Phase | Set | Ref |
|---|---|---|---|
| ASR | Before take-off | Aerodrome's altimeter setting (or its elevation, if not obtainable) | CAR 602.35 |
| ASR | En route | Nearest station along the route, or a station near the route if nearest stations are more than 150 NM apart | CAR 602.35 |
| ASR | Before descending to land | Aerodrome's altimeter setting, if obtainable | CAR 602.35 |
| SPR | Before take-off | Aerodrome's altimeter setting (or its elevation, if not obtainable) | CAR 602.36(1) |
| SPR | Before reaching the flight level of flight | 29.92" / 1013.2 mb | CAR 602.36(1) |
| SPR | Before descending to land | Aerodrome's altimeter setting, if obtainable (exceptions below) | CAR 602.36(1) |
SPR exceptions:
- Take-off, cruising above FL 180: may reset to standard at 18,000 ft ASL on the climb (TC AIM RAC 2.11).
- Holding: stay on standard. Switch to aerodrome setting only immediately before descending below the lowest flight level of the hold (CAR 602.36(2)).
- Descending from above FL 180: may reset to aerodrome-of-intended-landing setting when approaching FL 180, provided no holding or cruise below FL 180 is made or anticipated (TC AIM RAC 2.11(c)).
Crossing the boundary, unless ATC authorizes otherwise (CAR 602.37):
| From | Into | Set | When |
|---|---|---|---|
| ASR | SPR | 29.92" / 1013.2 mb | Immediately after entering the SPR |
| SPR | ASR | Nearest-station setting | Immediately before entering the ASR |
Trap: SPR is not just high-level airspace; low-level airspace outside ASR boundaries is SPR too.
References
- CAR 101.01(1)
- CAR 602.35
- CAR 602.36
- CAR 602.37
- TC AIM RAC 2.9
- TC AIM RAC 2.11