Flight operations were performed by the CL-84 in temperatures from –70 F to +90 F, and a range of ground manoeuvres, VTOL flight, hovering at various altitudes and transitions to and from conventional flight were made in winds gusting up to 35 knots (65 km/h). Handling qualities in these conditions were assessed as "exceptional". The effects of cg variations of 11 per cent mean aerodynamic chord were explored in hover, transition and low speed conventional flight.

The flight envelope was thoroughly explored, with the following points among the range covered:

Hovering at max design VTOL gross weight of 12,200 lb (5 534 kg) outside ground effect.

Flights to 150 knots (278 km/h) in transition with tail rotor operating and wing at approximately 10 degrees. Manoeuvres to 2g in transition.

Demonstration of 3g at 188 knots (348 km/h) EAS in the cruise, and 2g in turns at 300 knots (556 km/h) in a descent.

Demonstration of cross-shafting effectiveness in maintaining symmetric thrust with total instantaneous loss of power in one engine: a STOL landing was made following a real engine failure at 40 ft (12.2 m) at 27 knots (50 km/h) with wing at 40 degrees.

High speed of 265 knots.(491 km/h) TAS demonstrated at 8,000 ft (2,438 m).

Roll rate of better than 72 deg per second demonstrated.

On 12 September 1967, the CL-84 was lost. At 3,000 ft (914 m) and 150 knots (278 km/h) it entered an uncontrollable turn to port and took up a nose down attitude, successful ejection by the company’s chief pilot and flight test engineer being effected at about 2,000 ft (610 m). The subsequent investigation attributed the cause of the accident to the pitch mechanism of the port propeller, which allowed the propeller to go into fine pitch and cause the uncontrollable yaw. The basic configuration of the aircraft was in no way held to blame.

Up to the time of the accident, the CL-84 had made 305 flights totalling 145.5 hours (with another 260 hours of ground running time). The programme had included 346 VTOL sorties, 109 STOL sorties, 151 transitions and 25 conventional take-offs and landings.

Only two months before this accident, the CL-84 had been given a significant vote of confidence when the Canadian Armed Forces placed an order for three examples of a slightly improved version, known as the CL-84-1 to Canadair and CX-84 to the CAF. These three aircraft, which were to be used for an extensive programme intended "to determine the most effective roles of utility tilt-wing aircraft in the military environment", were basically similar to the CL-84 prototype but with some refinements. The 1,500 shp Lycoming LTCIK-4A engines offered seven per cent more power than available in the prototype; fuel capacity was increased to a total of 206 Imp gal (936 l), additional avionics were installed and two hard points were provided under the fuselage, to carry gun pods, rockets or two 100 Imp gal (455 l) drop tanks. Full dual control was provided, with North American LW-3B zero-zero ejection seats, although the aircraft was designed to be flown by one pilot if required; accommodation in the cabin was similar to that in the prototype, with a maximum of 12 occupants on inward-facing troop seats, or up to 1,250 lb (567 kg) of freight.

Further refinements of the basic design were proposed by Canadair at about the same time that the CX-84 programme got under way, these including the CL-84- 1C with 1,800 shp Lycoming LTCIS-2A engines and a fuselage lengthened by 11 in (0.28 m); the CL-84-ID with 1,800 hp Lycoming

T53-19A engines, enlarged fuselage and wide-track landing gear, and a version with General Electric T64 engines and bigger wing.

The $31.5 million (£13.1 million) cost of the programme to build and test the three CX-84s was shared in a 3:1 ratio by the Department of Industry, Trade and Commerce and Department of Defense, indicating Canadian interest in the possibilities of the basic aircraft configuration for commercial applications as well as military uses. To monitor the construction of the aircraft and plan for their evaluation, a strong military team was attached to Canadair in 1969 and its members worked closely on the programme with company personnel. However, much of the initial impetus of the programme was gradually lost, through changes in the official attitude towards the planned trials and a re-assessment of the potential value to the Canadian Armed Forces of VTOL aircraft such as the CX-84.

First flight of the CX-84* was made on 19 February 1970, nearly a year behind the original schedule date, and the second and third aircraft, both intended to have made their first flight in 1969 on the original test schedule, were completed only as back-up aircraft and have not been flown. With the decline in military interest, the first CX-84 is being used to complete a 150-hour schedule of manufacturer’s flight testing, and this was expected to be completed by the end of 1971. The second aircraft has completed a few hours of ground running and No 3 has been maintained as a stand-by at full modification status.