The Ar 77 had a thick cantilevered wooden wing which was skinned with plywood on the under-surfaces and covered with fabric on the upper surfaces. The fuselage was built up from welded steel tubing covered with fabric. Tail surfaces were built up from steel tubing and were also fabric covered,not following Arado's trademark layout of a fin and rudder forward of the tailplane;instead the tailplane was high mounted on the fin and supported by steel tube 'N' struts. Elevators and rudder were covered with fabric, aerodynamically balanced in the Ar 77A and without aerodynamic balance horns in the Ar 77B. The fixed tailwheel undercarriage consisted of cantilevered oleo-pneumatic main-leg struts fitted with brakes and a tail-wheel under the rear fuselage. The four crew members, being Pilot, Navigator or Instructor, and two Students, were accommodated in a cabin with full length windows along the fuselage sides.

The Arado Ar 77 was characterised by the relatively low placement of its engines in relationship to the wings. There was room for two people in the cockpit, and four other people, such as radio operators, in the fuselage. However, the Luftwaffe criticized the aircraft, instead, preferring the Focke-Wulf Fw 58.

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Arado "Ar 77" training and practice aircraft.
For conversion to multi-engine aircraft, the Arado aircraft manufacturers have developed a cantilever low-wing monoplane with two Argus AS-10 engines, offering space for a crew of four and equipped with a complete night flight system, including a flight control and direction finding system.
The two-spar wooden wing is connected to the main fuselage frames with four ball-and-socket bolt connections. The leading edge and underside up to the rear spar are covered with plywood, the remaining part is covered with fabric. There is an internal crossover between the upper chords of the two spars. The nose is made of sheet metal and is easily removable between the fuselage and the engine cowling. Landing flaps are located between the ailerons and the fuselage. The fuselage is welded from steel tubes, with a wooden fairing frame for attaching the fabric covering. The nose is covered with sheet metal. Two pilot seats side by side; after folding up the right seat, access to the Enclosed cabin with two or three seats. The cockpit canopy is detachable. The cabin canopy can be opened and locked in this position.

Metal tailplane, Meta II-planked fins, fabric-covered rudder. Both rudders have torsion bars, the horizontal stabilizer is attached to the keel and braced to the fuselage on each side by an N-rod. The rudder is equipped with counterweights and trim tabs.

Undercarriage is self-supporting, monopod-mounted. Each wheel is mounted on a spring strut attached to the front spar behind the engine. Compression rubber suspension with oil damping. 690 x 200 brakeable wheels, streamlined. Retractable tailwheel held in the center position by rubber bands. Dimensions: 290 x 110.

Powerplant: two Arg us-As-10 engines each 240 hp in the wing. Starting by hand crank or compressed air. A 170 l fuel tank is located for each engine between the spars near the fuselage. A steel oil tank is located in front of the firewall, and tubular coolers for recooling the lubricating oil are attached to the cylinder heads. Wingspan 19.2 m, length 12.6 m, height 3.25 m, area including fuselage 50.5 m², empty weight 2010 kg, take-off weight 2885 kg, wing loading 57.2 kg/m², power loading 6 kg/hp, maximum ground speed 243 km/h, cruising speed 202 km/h, landing speed 200 km/h. 84 km/h, climb time to 1000 m 3.9 min, to 2000 m 8.8 min, service ceiling 4900 m, range 720 km, flight time 3.5 h, fuel consumption 71 kg/h, corresponding to 45-50 l/100 km.

1 Pilot's seat
2 Rudder
3 Trim wheel
4 SUM AP 8 starting injection pumps
5 Mixture lever
6 Throttle lever
7 Fuel tank control and fire cock
8 Fire extinguisher pressure gauge 0-15 kg/cm3
Valves next to it
9 Control horn
10 Course sensor for the remote compass system
11 "Little Emil" pilot's compass
12 Coarse altimeter 0-8000 m
13 LGC 3 heading gyro
14 Artificial horizon
15 Electric tachometer 400-2400 rpm
16 Operating data panel
17 Instrument lamps
18 Lubricant temperature gauge 0-120°C
19 Lubricant pressure gauge 0-10 kg/cm3
20 Fuel pressure gauge 0-0.5 kg/cm3
21 Fuel level gauge 0-170 liters
22 Air pump for the fuel level gauge
23 Dual ignition switch

The list was reconstructed based on the available photo.
Not visible in the photo are the following devices installed on the left side of the pilot (derived from comparable contemporary aircraft types):
Onboard clock
Airspeed indicator 50-350 km/h
Pito heater indicator
Precise altimeter 0-1000 m
Course indicator
Statoscope variometer -10/+10 m/s
Turn indicator