TCAS II: Traffic Advisory System
How Traffic Advisories and Resolution Advisories actually work, the exact power/airspeed technique for each RA, and every inhibit altitude.
Source: AW169 / AW169 EP RFM Supplement 14 (Traffic Advisory System II — General Information, Resolution Advisory Manoeuvres, Limitations, Normal Procedures, Emergency and Malfunction Procedures). Verified identical between AW169 and AW169 EP.
What it does
The Rockwell Collins TCAS II monitors a nominal 14 NM radius around the helicopter, interrogating ICAO-compliant transponders on other aircraft. Hardware: a processor in the aft avionic bay and two directional antennas — one on top of the nose radome, one under the rear belly.
From the replies it computes range, bearing, closure rate, and altitude (if the intruder's transponder reports it) — from which it derives time to Closest Point of Approach (CPA), the main parameter driving alerts. It issues Traffic Advisories (TAs) to help the pilot visually acquire the intruder and prepare for a possible RA, and Resolution Advisories (RAs) that define a vertical maneuver to increase or maintain separation. If the intruder is also TCAS II-equipped, the two systems coordinate their RAs over Mode S data link so the resolution senses are complementary — not both aircraft climbing, for example.
Flying a Resolution Advisory
No banking maneuvers on an RA — fly to the indication on the VSI. If AFCS upper modes are engaged, press and hold the cyclic and collective FTR (Force Trim Release) buttons throughout the maneuver — this keeps the IAS and vertical-mode reference bugs synchronized with the aircraft's actual airspeed and altitude as you fly, rather than fighting the AFCS's prior targets.
| RA | Technique |
|---|---|
| Climb, IAS above 90 KIAS | Cyclic to reduce airspeed toward (not below) 90 KIAS, collective simultaneously to MCP 100% PI |
| Climb, IAS 90 KIAS or below | Collective to Take-Off Power, let IAS increase toward (not above) 90 KIAS |
| Descend | Collective to decrease torque as required — but not into autorotation; minimum 10% PI |
Limitations
Never maneuver on a TA alone — it is for visual acquisition, not a maneuver instruction. Compliance with an RA is mandatory, and the pilot is authorized to deviate temporarily from the current ATC clearance to comply with one — but not authorized to exceed the aircraft's flight envelope limits chasing an RA. TCAS II must be selected to TA ONLY during underslung load operations, and should be selected to TA ONLY with one engine inoperative (OEI) as well — reselect TA/RA once that condition no longer applies.
| Function | Inhibited below |
|---|---|
| Increase Descent RA | 1650 ft AGL climbing / 1450 ft AGL descending |
| Descend RA | 1200 ft AGL climbing / 1000 ft AGL descending |
| TA voice messages | 600 ft AGL climbing / 400 ft AGL descending |
| All RAs (reverts to TA only) | 1100 ft AGL climbing / 900 ft AGL descending |
| Climb RA | inhibited above 14,000 ft |
| Increase Climb RA | always inhibited |
What you see and hear
TA: PFD attitude indicator shows TRAFFIC flashing then steady amber, aural “Traffic, Traffic.” RA: PFD shows TRAFFIC flashing then steady red, plus a specific aural instruction and a climb/descend cue on the VSI — fly to keep the vertical speed needle inside the green arc. TCAS STBY / TCAS TEST / TCAS FAIL show as status-window messages on both PFD and MFD.