Selective radial scan: phase-of-flight instrument priority
Scanning (cross-checking): continuous, logical observation of flight instruments.
Radial scan:
- Attitude indicator is the hub: return to it after each other instrument, like spokes on a wheel.
Control vs performance:
| Type | Instruments | Role |
|---|---|---|
| Control | attitude indicator, tachometer (or manifold pressure gauge) | set attitude and power directly |
| Performance | altimeter, heading indicator | show how aircraft is behaving |
- Performance instrument shows unwanted change: correct with control instruments, then confirm on performance instruments (TP 1102).
Selective radial scan: look more often at instruments giving the task's needed information; less often at the rest, for backup. Ask continually:
- What information do I need?
- Which instruments give it?
- Is it reliable?
Straight-and-level example:
| Need | Main instrument | Cross-check (supporting) |
|---|---|---|
| Heading | heading indicator | turn co-ordinator, magnetic compass |
| Altitude | altimeter | vertical speed indicator, airspeed indicator |
- Supporting instruments confirm reliability; scanned less often than the main two.
Priority by phase of flight:
| Phase | Priority |
|---|---|
| Climbing toward assigned altitude | heading and airspeed lead |
| Nearing that altitude | airspeed matters less, altitude more; scan attitude indicator most, supported by heading indicator and altimeter |
| Levelling off, approaching cruise speed | airspeed matters again; scan airspeed indicator more, plus attitude indicator; still check heading indicator and altimeter often |
Trap: fixating on one instrument (altimeter reading 200 ft low) lets errors elsewhere, like heading drift, go unnoticed.
References
- TP 1102 Instrument Flying: Instrument Scan, The Selective Radial Scan, Applying the Scanning Pattern