The PM.1 was designed by students at the Instituto di Construzioni Aeronautische del Regio Politecnico di Milano in a 1938 competition for a modern, two seat light private training and sports aircraft. The name came from Polytechnic Milano. The prototype was built by CNA, first flying on 25 October 1939.

The PM.1 was a cantilever high wing monoplane. Its wing was straight tapered, with rounded tips and long span ailerons, built of wood with a plywood skin. The tailplane had a similar plan, placed on top of the fuselage with the trailing edge of the elevators in line with the rudder hinge so the rudder, which extended to the base of the fuselage, could move unimpeded. The fin and rudder were rounded and pointed; the rudder carried a trim tab.

The fuselage, also wooden and plywood covered, was flat sided, with car type doors giving access to the side-by-side seats in the cabin which was placed under the leading edge of the wing. In front, a compactly cowled, 40 kW (60 hp) CNA D.4 flat four engine drove a 2-blade propeller. The PM.1 had a conventional undercarriage with mainwheels on centrally mounted, faired V-form half axles and with vertical legs to the bottom longerons, assisted by a tailskid.

The outbreak of war and the need to concentrate on front-line aircraft delayed production of the PM.1 but an order for 10 was placed in August 1942. The partially completed aircraft were destroyed in an Allied bombing raid on Rome in July 1943; though the prototype avoided this event, it was destroyed later in the war. Its design influenced that of the post-war Macchi MB.308, though the latter has a tricycle undercarriage and a markedly revised tail.

Engine: 1 × CNA D.4 air-cooled flat four, 45 kW (60 hp)
Propeller: 2-bladed
Wingspan: 10.60 m (34 ft 9 in)
Length: 7.07 m (23 ft 2 in)
Height: 2.03 m (6 ft 8 in)
Wing area: 14.0 sq.m (151 sq ft)
Empty weight: 360 kg (794 lb)
Gross weight: 580 kg (1,279 lb)
Maximum speed: 180 km/h; 97 kn (112 mph)
Cruise speed: 154 km/h; 83 kn (96 mph)
Range: 600 km; 324 nmi (373 mi)
Service ceiling: 4,000 m (13,123 ft)
Time to altitude: 6 min to 1,000 m (3,280 ft)
Landing speed: 68 kmh; 36 kn (42 mph)
Crew: 2

During the 1920s the Compagnia Nazionale Aeronautica (CNA) were best known for their flying school in Rome, though they also manufactured experimental aircraft for the government. When they moved their Roman base from Cerveteri to Littorio in 1928, they built a factory in which they could produce both aircraft and aircraft engines; some were designed by other companies, some by themselves. The Eta was both CNA designed and powered.

The Eta was a conventional parasol wing light aircraft that could be configured as a single seater or with two seats in tandem; it could also be fitted with either a fixed conventional undercarriage or floats. It was originally powered by an uncowled, 9-cylinder CNA C-7 supercharged radial engine but later flew with an inverted 6-cylinder air-cooled supercharged inline, the CNA C.VI. The slightly tapered wing was mounted on tall faired parallel struts from the mid-fuselage, assisted by lighter diagonal struts and shorter, forward leaning supports from the upper fuselage. The single seat model placed the open cockpit just behind the wing trailing edge. The tail was conventional, with the tailplane on top of the fuselage and braced from below. The vertical surfaces were rounded. In keeping with the rest of the design, the fixed wheeled undercarriage was very simple, with unfaired wheels mounted on slender V-form struts attached to the lower fuselage.

The Eta was chiefly distinguished by setting three lightplane world records. At the time the FAI divided the lightest aircraft between to categories: C.II, single seats with empty weights less than 200 kg (41 lb) and C.I, two seaters weighing less than 400 kg (882 lb). These categories were then each sub-divided into landplane and seaplane. A 130 kW (170 hp) CNA C-7 engine had enabled a Fiat AS.1 to gain the Category I altitude record in December 1932 and on 6 November 1933 the single seat Eta, with the same motor and fitted with floats, set a new C.II record of 8,411 m (27.595 ft). It was then fitted with its wheeled undercarriage and flown to a new C.II landplane record of 10,008 m (32,835 ft) on December 1933. On both occasions the Eta was flown by Furio Niclot Doglio.

By 1936 the Eta was flying as a two seat seaplane. It is not known if these were different aircraft or the same one modified. Powered by the in-line, 112 kW (150 hp) CNA C-VI engine, on 15 May it set a new world C.I 100 km (62 mi) circuit speed record of 192.62 km/h (119.7 mph), flown by Gian Giacomo Chiesi with Domenico Rossetti.

Variants:

Category II
single seat, CNA C-7 engine, both landplane and seaplane.

Category I
two seat, CNA C.VI engine, both landplane seaplane.

Specifications:
tandem dual control, landplane
Engine: 1 × CNA C-7 9-cylinder supercharged radial, 130 kW (170 hp)
Propeller: 2-bladed
Wingspan: 10.0 m (32 ft 10 in)
Length: 6.50 m (21 ft 4 in)
Height: 2.49 m (8 ft 2 in)
Empty weight: 410 kg (904 lb)
Gross weight: 500 kg (1,102 lb)
Maximum speed: 219 km/h; 118 kn (136 mph)
Time to altitude: 25 min to 6,457 m (19,680 ft)
Landing speed: 65 km/h; 35 kn (40 mph)
Crew: 2