Piper PA-31 Navajo

Early Navajo with two-bladed propellers and two-part entry door

In 1962, Piper began developing a six- to eight-seat twin-engined corporate and commuter transport aircraft under the project name Inca, at the request of company founder William T. Piper.[2][4] Looking like a scaled-up PA-30 Twin Comanche, the PA-31 made its first flight on 30 September 1964, and was announced later that year.[1][4] It is a low-wing monoplane with a conventional tail, powered by two 310 hp (231 kW) Lycoming TIO-540-A turbocharged engines in "tiger shark" cowlings, a feature shared with the Twin Comanche and the PA-23 Aztec.[4][5][6]

As testing proceeded, two cabin windows were added to each fuselage side and the engines were moved further forward.[6][7] The PA-31, named "Navajo" after the native American tribe, was certified by the FAA on 24 February 1966, again in mid-1966 with an increase in maximum takeoff weight (MTOW) from 6,200 to 6,500 lb (2,812 to 2,948 kg), and deliveries began in 1967.[2][8]

The PA-31-300 was certified by the FAA in June 1967, the only variant without turbocharged engines: 300 hp (224 kW) Lycoming IO-540-M1A5 engines driving two-bladed propellers.[8] Unofficially, the initial model was referred to as the PA-31-310. Only 14 PA-31-300 were built in 1968 and 1969: the smallest variant production.[2][9]

Pressurized PA-31P with fewer and smaller windows

In January 1966, development of the PA-31P Pressurized Navajo had begun : Piper's first pressurized aircraft.[10] The PA-31P (or PA-31P-425 unofficially) was certified in late 1969.[11] It was powered by 425 hp (317 kW) Lycoming TIGO-541-E engines, had a longer nose, fewer and smaller windows, 25 US gal (95 L) fuel tanks in the engine nacelles and a one-piece airstair cabin entry door instead of the split pair of doors.[2][11][10] MTOW was increased to 7,800 lb (3,538 kg).[11] The PA-31P was produced from 1970 to 1977.[2]

The 1971 Navajo B featured air conditioning, new storage lockers in the rear of the engine nacelles, increased baggage space, a third door next to the cabin doors for easier baggage loading, and an optional separate door for the pilot to enter the cockpit.[3][12]

The PA-31-350 Chieftain, stretched by 2 ft (61 cm)

In September 1972, Piper unveiled the PA-31-350 Navajo Chieftain, a Navajo B stretched by 2 ft (61 cm) for up to ten seats, with more powerful engines and counter-rotating propellers to prevent critical engine handling problems.[8][13] The Chieftain was powered by 350 hp (261 kW) Lycoming TIO-540 variants, with an opposite-rotation LTIO-540 on the right-hand wing, and MTOW was increased to 7,000 lb (3,175 kg).[8] Deliveries started in 1973, after a delay due to a flood caused by Hurricane Agnes at Piper's factory in Lock Haven, Pennsylvania.[13][14]

The 1974 PA-31-325 Navajo C/R was base on the Navajo B.[15] The Navajo C/R had 325 hp (242 kW), lower rated versions of the Chieftain's counter-rotating engines.[8] It was certified in May 1974, and production commenced in the 1975 model year.[15] The Navajo B was also superseded in 1975 by the Navajo C.[15]

In May 1981, Piper established its T1000 Airliner Division at its Lakeland, Florida, factory.[16] The PA-31-350T1020 (or T1020) was a PA-31-350 Chieftain optimized for and marketed for the commuter airline market, without the 40 US gal (151 L) auxiliary fuel tanks in each wing.[8] Up to eleven seats could be fitted, and baggage capacity was reduced from 700 to 600 lb (318 to 272 kg) maximum.[8] The first T1020 was delivered in December 1981.[17]

The PA-31T3 (T1040) was a hybrid with the PA-31-350T1020 main fuselage, and the nose and tail of the PA-31T1 Cheyenne I.[18] The wings were similar to the Cheyenne I's, but with reduced fuel capacity and baggage lockers in the engine nacelles similar to those of the Chieftain.[11] An optional underbelly cargo pod was also available.[11][18] The Pratt & Whitney Canada PT6A-11 turboprop engines were the same as those of the Cheyenne I.[11] Deliveries began in July 1982.[17] A T1050 variant was proposed, with a fuselage stretch of 11 ft 6 in (3.51 m) and seating capacity for 17, but did not proceed.[18]

Pressurized PA-31P-350 Mojave

The PA-31P-350 Mojave was also a hybrid, a piston-engined Cheyenne.[19] The Mojave combined the Cheyenne I fuselage with the Chieftain tail.[19] The Chieftain's wings were strengthened, their span was 4 ft (1.2 m) wider and the fuel capacity was enlarged to 243 US gal (920 L).[19] The engines variants had intercoolers, and the rear part of the nacelles were baggage lockers.[19] The Mojave's MTOW rose by 200 lb (91 kg) to 7,200 lb (3,266 kg).[8][11] Certified in 1983, like the T1020 and T1040, the Mojave was produced in 1983 and 1984; combined production with the T1020 and T1040 was below 100 aircraft.[11][14][18] Two experimental PA-31-353s were also built in the mid-1980s.[14]

commuter cabin

PA-31 Navajo

Initial production version, also known unofficially as the PA-31-310.[2][8]

PA-31-300 Navajo

Variant of the Navajo with normally aspirated engines; 14 built.[2][9]

PA-31 Navajo B

Marketing name for 1971 improved variant with 310 hp (231 kW) Lycoming TIO-540-E turbo-charged piston engines, new airconditioning and optional pilot access door and optional wide utility door.[3]

PA-31 Navajo C

Marketing name for 1974 improved variant with 310 hp (231 kW) Lycoming TIO-540-A2C engines and other minor improvements.[3]

PA-31P Pressurized Navajo

Pressurized version of the PA-31 Navajo, powered by two 425-hp (317-kW) Lycoming TIGO-541-E1A piston engines.[2][11]

PA-31-325 Navajo

Referred to as the "Navajo C/R" for Counter-rotating; variant of Navajo with counter-rotating engines introduced with the PA-31-350 Chieftain. 325 hp (242 kW) Lycoming TIO-540 / LTIO-540 engines

PA-31-350 Chieftain

Stretched version of the Navajo with more powerful 350-hp (261-kW) counter-rotating engines (a Lycoming TIO-540 and a Lycoming LTIO-540) to eliminate critical engine issues.

PA-31P-350 Mojave

Piston-engined variant of the PA-31T1 Cheyenne I; 50 aircraft built.[11]

PA-31-350T1020

Also known as the T1020/T-1020; variant of the PA-31-350 Chieftain optimised for commuter airline use, with less baggage and fuel capacity and increased seating capacity (nine passengers). First flight September 25, 1981. 21 built.[8][25][26]

PA-31T3

Also known as the T1040/T-1040; turboprop-powered airliner with fuselage of the PA-31-350T1020, and wings, tail and Pratt & Whitney Canada PT6A-11 engines of PA-31T Cheyenne. First flight July 17, 1981. 24 built.[14][27]

PA-31-353

Experimental version of PA-31-350; two built.[14]

license-built EMB 820C

T1050

Unbuilt airliner variant with fuselage lengthened by 11 ft 6 in (3.51 m) compared to the PA-31-350.

EMB 820C

Version of Chieftain built under license by Embraer in Brazil.

Neiva Carajá

Turboprop conversion of EMB 820C, fitted with two Pratt & Whitney Canada PT6A-27 engines flat-rated to 550shp. The Carajá's MTOW of 8,003 pounds (3,630 kg) was 1,000 pounds (454 kg) more than that of the Chieftain.[24]

Panther conversion with four-blade propellers

Colemill Panther

Re-engined Navajo with 350 hp (261 kW) Lycoming TIO-540-J2B engines, four-blade Hartzell "Q-Tip" propellers and optional winglets. Conversion designed by Colemill Enterprises of Nashville, Tennessee.[28][29] The supplemental type certificates (STCs) were subsequently sold to Mike Jones Aircraft Sales, which continues to convert PA-31, PA-31-325 and PA-31-350 variants with Colemill-developed features.[30][31]

• December 3, 1983: SouthCentral Air Flight 59, a PA-31-350 registered N35206, carrying eight passengers and one pilot, was on the takeoff roll at Anchorage International Airport when it collided head-on with Korean Air Lines Flight 084, a McDonnell Douglas DC-10-30 freighter HL7339. The Piper struck the DC-10's left and center main landing gear and three passengers sustained minor injuries; the DC-10 overran the runway and the three crew suffered serious injuries. Investigators determined that the Korean Air Lines pilot had become disoriented taxiing in fog, failed to follow correct procedures and confirm his position, and accidentally initiated takeoff from the wrong runway. Both aircraft were severely damaged and were written off.[40]

• May 31, 2000: Whyalla Airlines Flight 904 was a scheduled commuter flight, operated by a Piper PA-31 Navajo which crashed while attempting to ditch in the Spencer Gulf, South Australia after suffering failures of both engines on the evening of 31 May 2000. All 8 people on board the aircraft were killed as a result of the accident. The findings of a subsequent investigation by the Australian Transport Safety Bureau highlighting the airline's operating procedures as a key factor leading to the accident were later overturned after they were contradicted by evidence presented at a coronial inquiry into the deaths of those on board the flight.[41] The safety implications arising from the accident were subject to a recall by engine manufacturer Textron Lycoming which saw close to 1000 aircraft grounded worldwide while defects were rectified at an estimated cost of $A66 million. Australia's aviation regulator, the Civil Aviation Safety Authority also mandated lifejackets be carried on all aircraft operating over water after the crash.[42]

Spain

• A PA-31P Pressurized Navajo formerly operated by the Spanish Air Force is on display at the Museo del Aire in Madrid.[38]

cockpit

PA-31-350 Navajo Chieftain

Data from Jane's All The World's Aircraft 1976–77 [43]

General characteristics

• Crew: 1 or 2
• Capacity: 5 to 7 passengers
• Length: 32 ft 7+1⁄2 in (9.94 m)
• Wingspan: 40 ft 8 in (12.40 m)
• Height: 13 ft 0 in (3.96 m)
• Wing area: 229 sq ft (21.3 m²)
• Airfoil: NACA 63₄415 at root, 63₁212
• Empty weight: 3,930 lb (1,783 kg)
• Max takeoff weight: 6,500 lb (2,948 kg)
• Fuel capacity: 190 US gal (160 imp gal; 720 L) total, 187 US gal (156 imp gal; 710 L) useable
• Powerplant: 2 × Lycoming TIO-540-A air-cooled six-cylinder horizontally opposed piston engine, 310 hp (230 kW) each
• Propellers: 3-bladed Hartzell metal, fully feathering propellers, 6 ft 8 in (2.03 m) diameter

Performance

• Maximum speed: 261 mph (420 km/h, 227 kn) at 15,000 ft (4,600 m)
• Cruise speed: 238 mph (383 km/h, 207 kn) at 20,000 ft (6,100 m) (econ. cruise)
• Stall speed: 73 mph (117 km/h, 63 kn) (flaps down)
• Never exceed speed: 272 mph (438 km/h, 236 kn) [8]
• Range: 1,165 mi (1,875 km, 1,012 nmi) at 20,000 ft (6,100 m) (econ. cruise speed)
• Service ceiling: 26,300 ft (8,000 m)
• Rate of climb: 1,445 ft/min (7.34 m/s)

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