Wishing to remain an independent aircraft manufac­turer in the UK Handley Page saw a market in the 1960s for a turboprop powered commuter aircraft somewhat larger than the Beechcraft King Air, Turbo Commander and Swearingen Merlin II. This became the HP137 Jetstream. After Handley Page went bankrupt, Scottish Aviation took over produc­tion, which then ended in 1975. The deregulation of the airlines in the USA at the end of the 1970s brought a new demand, which British Aerospace was willing to satisfy with a revived version of the Jetstream. This was easy as Scot­tish Aviation had been absorbed into the company. 

The Jetstream has a relatively wide, circular fuselage, with quite a long, pointed nose. Together with the seven flat cockpit windows it gives the aircraft a charac­te­ristic front appearance. The fuselage has large oval cabin windows, in portrait mode. The tail is of a cruci­form design. The main gear has single wheels and retracts sideways in the wings. The nose gear has two wheels and retracts forward in the nose.

The different versions of the Jetstream can be identified by looking at:

• the shape of the engine nacelles
• the number of propeller blades
• the shape of the nose
• the presence of eyebrow cockpit windows
• the presence of an overwing emergency exit on the left side
• the presence of a radome underneath the fuselage

All these Jetstream versions are powered by a variant of the Turbomeca Astazou engine. These are recognised by the shape of the engine nacelles: they have a ring-shaped air intake quite distant from the tip of the propeller spinner. Additionally, there is a smaller cooler intake at the bottom of the nacelles. The Jetstream II has higher power engine than the Jetstream I; Jetstream 200 is the marketing name of the Jetstream II built by Scottish Aviation. There seem to be no external differences.

These aircraft were multi engine trainers for the Royal Air Force. They are the same as the Jetstream I, except for the eyebrow cockpit windows.

The Royal Navy used converted Jetstream T1s for training observers. Hence these Jetstream T2s are equipped with a radar in the longer nose. They also have a wire antenna from the top of the cockpit to the tail.

Handley Page had received a contract from the United States Air Force to deliver Jetstreams as small transport aircraft. These had the designation C-10A. However, none were delivered as the order was cancelled. Just one Jetstream 3M prototype was built. It has Garrett TPE331 engines like the later Jetstream 31, but with air intakes below the propellers. These props had only three blades. The double cabin doors that were planned for the C-10A were not yet placed.

Jack Riley, known amongst others for converting DH104 Doves with more modern engines, was one of the driving forces behind the HP137 development. While he selected the Turbo­meca Astazou engine, it proved a non-optimal choice. Therefore he offered a conversion with Pratt & Whitney PT6A engines. These Riley Jetstreams can be recognised by nacelles with an air intake at the bottom and exhausts at each side, just behind the prop.

Century Aircraft offered another engine conversion of the original HP137s. They used the TPE331 engines, in the same upside down configuration as the later Jetstream 31. So the air intake is on top of the nacelle as well. However, the shape of the nacelle is different, having a flatter bottom and more curved top than on the Jetstream 31s with the highest point further aft. They have three blade props.

To capture a part of the market created by the deregulation of air transport in the United States, British Aerospace revived the Jetstream. It fitted it with TPE331 engines, with air intakes above the propellers. The nacelles are more streamlined than those of the Jetstream III though. Moreover, the engines have four blade props. Jetstream 31s can optionally be fitted with a cargo/bagge pod underneath the fuselage.

For each country British Aerospace had to slightly adapt the basic model. The model numbers used were 01 for United States, 02 for United Kingdom, 03 for Germany, 07 for Australia, 08 for the Netherlands, 09 for Italy, 10 for Sweden, 12 for Canada and 16 for Switzerland.

An improved version of the Jetstream 31 is called the Jetstream 32. It has more powerful engines, but that is not visible on the outside. However, the Jetstream 32 has an overwing emergency on the left hand side as well, while earlier models only have it on the right side. Like the Series 31 many have a bagage pod underneath the fuselage, but not all.

For each country British Aerospace had to slightly adapt the basic model. The model numbers used were 01 for United States, 02 for United Kingdom, 06 for France, 07 for Australia, 12 for Canada, 16 for Switzerland and 17 for Japan.

The Royal Navy also acquired a training version of the Jetstream 31, which it designated Jetstream T3. The T Mark 3 can be distinguished from the T Mark 2 by the engine nacelles, standard nose and radome underneath the middle of the fuselage. Compared to the standard Jetstream 31 is has a radome, wire antenna and eyebrow cockpit windows.

The Jetstream T3 has the Jetstream 31's engines and nose, but eyebrow cockpit windows and a radome under the fuselage. (photo: Mike Freer - Touchdown Aviation/WikiMedia)