During the beginning of the 1960s Beechcraft brought the first modern eight to ten seat twin prop plane on the market, the Queen Air. Cessna did not stay behind and started the 400 series, starting with the Cessna 411. All are low wing, low horizontal stabiliser aircraft, with two piston or turboprop engines in the wing's leading edge. The single wheel main landing gear retracts sidewards into the wings. Most versions have large oval cabin windows although later Cessna started using rectangular ones. These models are described on a separate page.

The different versions of the oval cabin window Cessna 400 series can be recognised by

• the shape and number of the cockpit windows
• the number of cabin windows
• the shape of the nose
• the shape of the engine nacelles
• the number of propeller blades
• the presence of tip tanks
• the presence of winglets
• the dihedral of the horizontal stabilisers

Model 401 was actually not the first of the family, but derived from the 411. The 401 is a non-pressurised aircraft, which can be noted from the cockpit side windows: they do not have a small triangular window in between the front and side window (see detail photo above). So there are four cockpit windows. The 401 has four oval cabin windows on each side, and an airstair door on the left side. A sidewards opening extra door is optional. The latter can be recognised by two hinge fairings.
Another feature of the 401 is the wide-chord vertical tail, which is about as wide as it is high. In front is a narrow dorsal fin with a tiny opening at the root. Finally, the Cessna 401 has tip tanks and non-geared engines. The drive shaft is more less centered in the nacelle when viewed from the side (see detail photo above).

Compared to the Cessna 401 model 401A has minor changes we could not spot on the outside. Similarly, the Cessna 401B also has some small improvements.

The Cessna 402 is externally the same as the 401. It has a reinforced bonded-honeycomb floor, for heavier duty use.

The main difference between the Cessna 402A and the original Cessna 402 is the lengthened nose, with a larger baggage compartment. Look for the larger distance between the nose cone and nose gear for distinction. A crew entry door, in the right cockpit side window, is optional.

In another upgrade the Cessna 402A became the 402B, which initially only minor changes. From the 1973 model on it has an increased cabin volume and five rectangular cabin windows on each side. This version is described separately.

This was the ‘founding member’ of the Cessna 400 series. It is generally similar to the Cessna 401, regarding the cockpit windows, four cabin windows and tip tanks. Different though is the vertical stabiliser, which is fairly shallow: it is higher than it is tall. Additionally, the engines are geared, which means that the drive shaft lies slightly on top of the nacelle when viewed from the side, much like on the 421B/421C. The baggage compartment in the nose can only be accessed from the left side. It is immediately after the nose cone. On right side of the nose there are only panels to get access to systems.

This version is the same as the Cessna 411 but then with a redesigned nose to hold more baggage. The baggage door is placed further aft than on the 411, at about 80 cm from the nose, and at both sides. The length of the nose is the same though. Some examples have a less pointed, but unfortunately it does not apply to all 411As.

The Cessna 414A is similar in appearance to the Cessna 421C: five oval cabin windows, a long pointed nose, a higher vertical stabiliser and no tip tanks. However, the prop spinner (and drive shaft) is in the middle of the engine, typical for non-geared engines (see detail photo above).

The Cessna 411A was fitted with a pressurised cabin and also has the broader vertical tail like the 401/402. Like the 414 it has small triangular cockpit side windows, a feature of the pressurised cabin. Also the small intake at the root of the drosal fin is gone. The Cessna 421 equipped with geared engines (see detail photo above for characteristics).

The Cessna 421 has a short nose, a small triangular cockpit side window, geared engines and tip tanks. (photo G B_NZ/WikiMedia)

The Cessna 421A is supposed to be three inches longer than the Cessna 421, but do you see the difference? (photo Peter Bakema/WikiMedia)

Remove the tip tanks from a late model 421B and make the vertical tail higher, and you get a 421C. At least from the outside. From the 1981 model is also has a trailing link main landing gear instead of a straight one. The main gear doors then also got a different shape.

From the outside the Cessna 425 at first looks like another Cessna 421C converted with turboprops driving three-bladed or four-bladed props. However, the horizontal stabilisers have a significant dihedral, whereas that of the older (converted) pistons is straight. The nose is somewhat more blunt as well.

Corsair was the name of the original version. A factory upgraded version with more cabin space and a higher maximum takeoff weight is called Conquest I.

This is a remanufactured Cessna 421C with Pratt & Whitney PT6A-135A turboprop engines, Garmin G600 avionics, winglets and different aircraft systems. It can be distin­guished from other 421Cs with turboprops and winglets by its five bladed props. Only one seems to be partially converted before the project was put on hold.

The Cessna 414A modified by RAM Aircraft with winglets is called RAM/Cessna 414AW. Some also received a blunt nose.

This is a conversion of Cessna 421B/Cs with two Lycoming LTP101 turboprop engines by Riley. These have "pitot style" air intakes below the spinners, slightly separated from the spinner. The single exhaust is at the end of the nacelle, behind the wing's leading edge.

Later the conversion was marketed at Turbine Rocket 421. The designations are R421BL and R421CL for conversions of 421B and C respectively.

The Riley Turbine Eagle 421 has a secondary intake at the bottom of the nacelles. (photo: Oyoyoy/WikiMedia)

This is a conversion of Cessna 402s with two Allison 250 turboprop engines instead of the pistons, in long, slender nacelles. It has two exhausts underneath the nacelle, in front of the wing leading edge. The conversions was developed by American Jet Industries and could also be done on the 401.