Swedish Air Force designation: Tp88
US military designation: C-26A/B
TYPE: Twin-turboprop 19/20-passenger commuter airliner.
PROGRAMME: Metro III originally SFAR 41 approved; FAR 23 type approval June 1990 for version with TPE331-11 engines and September 1990 for Metro 23 with TPE331-12s; both types to remain in production under SFAR 41 until October 1991 when Metro III will be discontinued. British CAA certification August 1988; required modifications included dual-redundant stall warning system, dual continuous water/alcohol/water injection system, modified aileron aerofoil section, externally operable escape hatches.
VARIANTS: SA227-DC Metro 23: Current high gross weight aircraft.
Tp88: Swedish Air Force VIP transport; one delivered.
C-26A and C-26B: Six C-26As ordered March 1988 as US Air National Guard Operational Support Transport Aircraft (ANGOSTA), later increased to 13, delivered from March 1989; 10 delivered by 1 May 1990; one plus nine C-26Bs ordered FY 1990; these have quick-change passenger, medevac or cargo interiors and are due to be delivered by September 1995. Contract awarded January 1991 by USAF Aeronautical Systems Division for delivery/logistics support of up to 53 C-26s over five-year period from January 1992.
Expediter I: All-cargo version; air-conditioning ducts moved to increase cargo volume, reinforced cabin floor, cargo nets and guards; reduced empty weight allowing max payload of more than 2,268 kg (5,000 lb); first operator SAT-AIR on behalf of United Parcel Service; first of 10 Expediter Is delivered to DHL Worldwide Courier Express April 1985 with structurally reinforced landing gear and wing main spar for max T-O weight 7,257 kg (16,000 lb).
Merlin 23: Business aircraft version of Metro 23; launched November 1990 at RAA Fall Meeting, Phoenix, Arizona; meets new FAR 23 commuter certification requirements effective October 1991.
DESIGN FEATURES: Certificated to FAA SFAR 41 and 41B, which covers ICAO Annex 8, for operation at T-O weight over 5,670 kg (12,500 lb); Metro III cleared for T-O weight 6,577 kg ( 14,500 lb); optional high gross weight version 7,257 kg (16,000 lb). Metro 23, to which listed figures apply, has max T-O weight of 7,484 kg (16,500 lb).
Changes from Metro II include 3.05 m (10 ft 0 in) increase in wing span, improved handling, more powerful engines with slow-turning four-blade propellers, new main gear doors for better take-off and landing performance and easier maintenance, new streamlined nacelles with petal doors and quick-action latches, new fire prevention and containment with flammable fluid pipework isolated from electrical components and wiring. Certificated for flight into known icing; lightning strike protection claimed to be equal to that of latest commercial jet transports.
Wing section NACA 652A215 at root, 642A415 at tip; dihedral 5°; incidence 1° at root, -2° 30' at tip; sweepback at quarter-chord 0° 54'. Goodrich automatic, bleed air operated pneumatic de-icing boots on wing, tailplane and fin.
FLYING CONTROLS: Mechanically operated, aerodynamically and mass balanced; manual trim tab in each aileron; electrically operated variable incidence tailplane; manual rudder trim tab; small ventral fin. Hydraulically operated double-slotted trailing-edge flaps.
STRUCTURE: Two-spar fail-safe wing made in one piece; main spar beams have laminated caps (titanium laminations in centre-section); pressurised cylindrical fuselage of 2024 aluminium alloy, flush riveted; glassfibre honeycomb nose cap can contain 0.46 m (18 in) diameter weather radar antenna.
LANDING GEAR: Retractable tricycle type with twin wheels on each unit. Hydraulic retraction, with dual actuators on each unit. All wheels retract forward, main gear into engine nacelles, nosewheels into fuselage Ozone Aircraft Systems oleo-pneumatic shock absorber struts. Nosewheel steerable (±63° max). Free-fall emergency extension, with backup of hand operated hydraulic pump. Goodrich mainwheels with low-pressure tubeless tyres, size 19.5 x 6.75-8, type VII. Jay-Em nosewheels and Goodyear low-pressure tubeless tyres, size 18 x 4.40, type VII. Tyre pressures: nosewheel at standard T-O weight 3.79 bars (55 lb/sq in), at optional increased T-O weight 4.76 bars (69 lb/sq in); mainwheels at standard T-O weight 5.60 bars (87 lb/sq in), at optional T-O weight 7.10 bars (103 lb/sq in). Goodrich self-adjusting hydraulically operated disc brakes and anti-skid system.
POWER PLANT: Metro III has two 745.5 kW (1,000 shp) dry Garrett TPE331-11U-612G turboprops with propeller reversing. SA227-DC, C-26 and Metro 23 have TPE331-12UA-701GS giving 745.5 kW (1,000 shp) dry and 820 kW (1,100 shp) with continuous alcohol/water injection system, driving a McCauley four-blade constant-speed lully feathering reversible-pitch metal propeller. Automatic propeller synchrophasing standard. In-flight windmill start capability. Integral fuel tank in each wing, each with a usable capacity of 1,226 litres (324 US gallons; 270 Imp gallons). Total usable fuel capacity 2,452 litres (648 US gallons; 540 Imp gallons). Refuelling point in each outer wing panel. Automatic fuel heating. Oil capacity 15.1 litres (4 US gallons; 3.3 Imp gallons). Alcohol/water tank in nose (except Metro III), capacity 60.5 litres (16 US gallons; 13.3 Imp gallons), with two pumps to pump fluid to engines. Engine inlet de-icing by bleed air. Electric oil cooler inlet anti-icing. Electric propeller de-icing. Flush mounted fuel vents. Single-point rapid defuelling provisions. Negative torque sensing, single red line/autostart, automatic engine temperature limiting, and engine fire extinguishing systems.
ACCOMMODATION: Crew of two on flight deck, each with four-way adjustable seat with folding armrests and shoulder harness, separated from passenger/cargo area by partial bulkhead on port side and armrest height curtain on starboard side. Dual controls standard. Bulkhead between cabin and flight deck optional. Standard accommodation for 19-20 passengers seated two abreast, on each side of centre aisle. 'No smoking' and 'Fasten seat belt' signs. High-back, tracking, quickly removable passenger seats standard. Interior convertible to all-cargo or mixed passenger/cargo configuration with movable bulkhead between passenger and cargo sections. Snap-in carpeting. Self-stowing aisle filler. Tiedown fittings for cargo at 0.76 m (30 in) spacing. Integral-step passenger door on port side of fuselage, immediately aft of flight deck. Large cargo loading door on port side of fuselage at rear of cabin, hinged at top. Three window emergency exits, one on the port, two on the starboard side. Forward baggage/avionics compartment in nose, capacity 363 kg (800 lb). Pressurised rear cargo compartment, capacity 385 kg (850 lb). Cabin air-conditioned and pressurised. Electric windscreen de-icing. Two-speed windscreen wipers.
SYSTEMS: AiResearch automatic cabin pressure control system: max differential 0.48 bar (7.0 lb/sq in), providing a sea level cabin altitude to 5.120 m (16.800 ft). Engine bleed air heating, dual air cycle cooling system, with automatic temperature control. Air blower system for on-ground ventilation. Independent hydraulic system for brakes. Dual engine driven hydraulic pumps, using fire resistant MIL-H-83282 hydraulic fluid, provide 138 bars (2,000 lb/sq in) to operate flaps, landing gear actuators and nosewheel steering. Hydraulic system flow rates 30.3 litres (8 US gallons; 6.7 Imp gallons)/min at idle power, both engines; 46.7 litres (12.34 US gallons; 10.27 Imp gallons)/min at T-O and climb power. Air/oil reservoir, pressure 2.27 bars (33 lb/sq in). Electrical system supplied by two 300A 28V DC starter/generators. Fail-safe system with overload and overvoltage protection. Redundant circuits for essential systems. Two 350VA solid state inverters supply 115V and 26V AC. Two SAFT 24V 23Ah nickel-cadmium batteries for main services. Engine fire detection system and fire extinguishing system standard. Wing overheat detection system. Oxygen system of 1.39 m³ (49 cu ft) capacity with flush outlets at each seat; system with capacity of 5.04 m³ (178 cu ft) optional. Stall avoidance system comprising angle indicator, visual and aural warning.
AVIONICS: Two flight deck and four cabin speakers standard; provisions for installation of remotely mounted or panel mounted avionics, customer furnished weather radar and autopilot.
EQUIPMENT: Standard equipment includes pilot and co-pilot foot warmers; edge lit consoles, pedestal and switch panels; integrally lit instruments; annunciator panel with 48 indicators; internally operated control locks, individual reading lights and air vents for each passenger; heated pitot; heated static sources; baggage compartment, cargo compartment, entrance, map and instrument panel, ice inspection, retractable landing, navigation, rotating beacon and taxi lights; automatic engine start cycle; external power socket; and static wicks.
DIMENSIONS, EXTERNAL:
- Wing span: 17.37 m (57 ft 0 in)
- Wing mean aerodynamic chord: 1.84 m (6 ft 0⅓ in)
- Wing aspect ratio: 10.5
- Length overall: 18.09 m (59 ft 4¼ in)
- Height overall: 5.08 m (16 ft 8 in)
- Tailplane span: 4.86 m (15 ft 11½ in)
- Wheel track: 4.57 m (15 ft 0 in)
- Wheelbase: 5.83 m (19 ft 1½ in)
- Propeller diameter: 2.69 m (8 ft 10 in)
- Passenger door (fwd): Height: 1.35 m (4 ft 5 in)
- Width: 0.64 m (2 ft 1 in)
- Cargo door (rear): Height: 1.30 m (4 ft 3¼ in)
- Width: 1.35 m (4 ft 5 in)
- Height to sill: 1.30 m (4 ft 3¼ in)
- Forward baggage doors (two, each):
- Height: 0.64 m (2 ft 1 in)
- Width: 0.46 m (1 ft 6 in)
- Emergency exits (three, each):
- Height: 0.71 m (2 ft 4 in)
- Width: 0.51 m (1 ft 8 in)
DIMENSIONS, INTERNAL:
- Cabin, excl flight deck and rear cargo compartment:
- Length: 7.75 m (25 ft 5 in)
- Max width: 1.57 m (5 ft 2 in)
- Max height (aisle): 1.45 m (4 ft 9 in)
- Floor area: 13.01 m² (140.0 sq ft)
- Volume: 13.88 m³ (490.0 cu ft)
- Rear cargo compartment (pressurised):
- Length: 2.34 m (7 ft 8 in)
- Max width: 1.57 m (5 ft 2 in)
- Max height: 1.32 m (4 ft 4 in)
- Volume: 4.06 m³ (143.5 cu ft)
- Nose cargo compartment (unpressurised):
- Length: 1.75 m (5 ft 9 in)
- Volume: 0.85 m³ (30.0 cu ft)
AREAS:
- Wings, gross: 28.71 m² (309.0 sq ft)
- Ailerons (total): 1.31 m² (14.12 sq ft)
- Trailing-edge flaps (total): 3.78 m² (40.66 sq ft)
- Fin, incl dorsal fin: 3.40 m² (36.62 sq ft)
- Rudder, incl tab: 1.80 m² (19.38 sq ft)
- Tailplane: 5.08 m² (54.70 sq ft)
- Elevators: 1.98 m² (21.27 sq ft)
WEIGHTS AND LOADINGS (Metro 23):
- Operating weight empty: 3,935 kg (8,675 lb)
- Max fuel weight: 1,969 kg (4,342 lb)
- Max T-O weight: 7,484 kg (16,500 lb)
- Max ramp weight: 7,530 kg (16,600 lb)
- Max zero-fuel weight: 6,577 kg (14,500 lb)
- Max landing weight: 7,110 kg (15,675 lb)
- Max wing loading: 261 kg/m² (53.3 lb/sq ft)
- Max power loading: 4.56 kg/kW (7.5 lb/shp)
PERFORMANCE (Metro 23 at max T-O weight of 7,484 kg; 16,500 lb, ISA, except where indicated):
- Design diving speed (VD): 311 knots (576 km/h; 358 mph) CAS
- Max operating speed (VMO): 248 knots (459 km/h; 285 mph) CAS
- Max operating Mach No.(MMO): 0.52
- Max cruising speed at 97% rpm, bleed low, max T-O weight at 3,353 m (11,000 ft): 288 knots (534 km/h; 331 mph)
- Stalling speed:
- flaps and wheels up: 103 knots (191 km/h; 118 mph) IAS
- flaps and wheels down: 89 knots (165 km/h; 102 mph) IAS
- Max rate of climb at S/L, bleed open: 698 m (2,290 ft )/min
- Rate of climb at S/L, one engine out, bleed closed: 176 m (580 ft)/min
- Service ceiling: 7,666 m (25,150 ft)
- Service ceiling, one engine out: 3,505 m (11,500 ft)
- T-O to 15 m (50 ft), wet power: 1,414 m (4,640 ft)
- Landing run: 843 m (2,765 ft)
- Range:
- with 19 passengers and baggage, FAA IFR reserves: over 782 nm (1,450 km; 900 miles)
- with 2,720 kg (6,000 lb), FAA IFR reserves: over 520 nm (967 km; 600 miles)
- C-26 with 1,315 kg (2,900 lb) payload, 1,969 kg (4,342 lb) fuel, no reserves: 1,740 nm (3,223 km; 2,000 miles)
