Applying a CRFI report
A reported CRFI (Canadian Runway Friction Index) corrects two things only:
- Landing distance
- Crosswind limit
No take-off correction: see contaminated-takeoff-reject-point. Expected CRFI by surface: crfi-expected-by-surface.
Contamination (water, snow, ice) drops tire-to-runway friction coefficient substantially:
- Stop portion of accelerate-stop distance increases.
- Landing distance increases.
- Crosswind may cause directional control difficulties.
Landing distance, Table 1.3:
- Take aircraft's dry, unfactored landing distance; read across to reported CRFI column.
- Lower CRFI (poorer braking) always gives longer corrected distance.
- Example: 2000 ft dry becomes 3480 ft at CRFI 0.60 (best braking tabulated), 5250 ft at CRFI 0.18 (worst tabulated).
- Stated to 95% level of confidence: conservative in more than 19 of 20 landings, for properly executed landings.
- Separate Table 1.4 for aircraft with discing or reverse thrust. Light single with neither always uses Table 1.3.
Tables 1.3 and 1.4 are guidance, not regulation (TC AIM AIR 1.6.7):
- Compiled from field-test data.
- Do not change regulatory requirements.
- Used at pilot's discretion.
- Onus for wet or contaminated runway information, guidance or advice rests with aircraft manufacturer, not TC AIM.
More Table 1.3 rows (no discing/reverse thrust): dry unfactored landing distance vs recommended distance at CRFI 0.60 / 0.30 / 0.18, plus equivalent dry landing field length at 60% and 70% factor.
| Dry LDG (ft) | CRFI 0.60 | CRFI 0.30 | CRFI 0.18 | LFL @60% | LFL @70% |
|---|---|---|---|---|---|
| 1 800 | 3 120 | 3 900 | 4 620 | 3 000 | 2 571 |
| 2 200 | 3 720 | 4 750 | 5 700 | 3 667 | 3 143 |
| 2 400 | 4 100 | 5 260 | 6 300 | 4 000 | 3 429 |
| 2 600 | 4 450 | 5 740 | 6 870 | 4 333 | 3 714 |
| 2 800 | 4 760 | 6 150 | 7 360 | 4 667 | 4 000 |
| 3 000 | 5 070 | 6 590 | 7 920 | 5 000 | 4 286 |
| 3 200 | 5 450 | 7 130 | 8 600 | 5 333 | 4 571 |
| 3 400 | 5 740 | 7 550 | 9 130 | 5 667 | 4 857 |
| 3 600 | 6 050 | 7 990 | 9 680 | 6 000 | 5 143 |
| 3 800 | 6 340 | 8 410 | 10 220 | 6 333 | 5 429 |
| 4 000 | 6 550 | 8 700 | 10 580 | 6 667 | 5 714 |
Table 1.3 assumes standard minimum-distance landing from 50 ft:
- Stabilized approach at
VRef, 3 degree glideslope to 50 ft or lower. - Firm touchdown.
- Minimum delay to nose lowering.
- Minimum delay to ground lift dump and brakes.
- Sustained maximum antiskid braking until stopped.
Landing field length:
- Turbojets: landing distance / 0.6.
- Turboprops: landing distance / 0.7.
- AFM gives landing distance: enter Table 1.3 from left-hand column.
- AFM gives landing field length: enter from right-hand columns.
Crosswind limit, Figure 1.1:
- Reported CRFI sets recommended maximum crosswind component.
- Figure 1.1 uses different CRFI increments than Tables 1.3 and 1.4; CRFI values identical.
- TC AIM example: CYOW reports CRFI 0.30; tower wind 40 degrees off runway at 20 kt = 15 kt headwind, 13 kt crosswind component.
- Recommended minimum CRFI for 13 kt crosswind: 0.35. CRFI 0.30 risks uncontrollable drifting and yawing.
Trap: CRFI 0.30 is not enough for a 13 kt crosswind; Figure 1.1 recommends at least 0.35.
References
- TC AIM AIR 1.6.7 (CRFI application to aircraft performance: Table 1.3, Figure 1.1)