In the 1970s, de Havilland Canada had invested heavily in its Dash 7 project, concentrating on STOL and short-field performance, the company's traditional area of expertise.

Using four medium-power engines with large, four-bladed propellers resulted in comparatively lower noise levels, which combined with its excellent STOL characteristics, made the Dash 7 suitable for operating from small in-city airports, a market DHC felt would be compelling.

However, only a handful of air carriers employed the Dash 7, as most regional airlines were more concerned about the operational costs (fuel and maintenance) of four engines, rather than the benefits of short-field performance.

In 1980, de Havilland responded by dropping the short-field performance requirement and adapting the basic Dash 7 layout to use only two, more powerful engines.

[citation needed] Air Canada was a crown corporation at the time, and both Boeing and Airbus were competing heavily via political channels for the contract.

Allegations of secret commissions paid to Prime Minister of Canada Brian Mulroney are today known as the Airbus affair.

Following its failure in the competition,[citation needed] Boeing immediately put de Havilland Canada up for sale.

A deal with its machinists union in June 2017 allowed the assembly of the wings and cockpit section outside Canada and searches for potential partners commenced.

[10] Bombardier expected to produce the cockpit section in its plant in Queretaro, Mexico, outsourcing the wings to China's Shenyang Aircraft Corp, which already builds the Q400's centre fuselage.

[16] In July 2010, Bombardier's vice president, Phillipe Poutissou, made comments explaining the company was still studying the prospects of designing the Q400X and talking with potential customers.

[20] At the February 2016 Singapore Airshow, Bombardier announced a high-density, 90-seat layout of the Q400, which would enter service in 2018; keeping the 28 in (71 cm) seat pitch of the Nok Air 86-seats, an extra row of seats is allowed by changing the configuration of the front right door and moving back the aft pressure bulkhead.

[23] On November 8, 2018, Canadian company Longview Aviation Capital Corporation, through its subsidiary Viking Air, acquired the entire Dash 8 program and the de Havilland brand from Bombardier, in a deal that would close by the second half of 2019.

[30] On June 3, 2019, the sale was closed with the newly formed De Havilland Canada (DHC) taking control of the Dash 8 program, including servicing the previous -100, -200, and -300 series.

[31] There were 17 Dash 8s scheduled for delivery in 2021, and De Havilland planned to pause production after those, while the factory lease expired in 2023.

[32] On February 17, 2021, DHC announced a pause in production, planned for the second half of 2021, due to a lack of Dash 8 orders from airlines.

[34] In July 2022, DHC announced that it would review the Dash 8 programme and supply chain later in the year, and could restart production in the middle of the decade if conditions allowed.

[35] At the Farnborough International Airshow in July 2024, DHC announced orders for seven Series 400 aircraft, including one for Skyward Express, two for Widerøe, and one for the Tanzania Government Flight Agency.

[39] Distinguishing features of the Dash 8 design are the large T-tail intended to keep the tail free of prop wash during takeoff, a very high aspect ratio wing, the elongated engine nacelles also holding the rearward-folding landing gear, and the pointed nose profile.

The Q400 has a cruising speed close to that of most regional jets, and its mature engines and systems require less frequent maintenance, reducing its disadvantage.

[64] In September 2007, two separate accidents of similar landing gear failures occurred within four days of each other on Scandinavian Airlines (SAS) Dash 8-Q400 aircraft.

Shortly after touchdown, the right main gear collapsed and the airliner skidded off the runway while fragments of the right propeller shot against the cabin, and the right engine caught fire.

[93] In a press release on October 28, 2007, the company's president said: "Confidence in the Q400 has diminished considerably and our customers are becoming increasingly doubtful about flying in this type of aircraft.

"[91][93][94] The preliminary Danish investigation determined the latest Q400 incident was unrelated to the airline's earlier corrosion problems, in this particular case caused by a misplaced O-ring found blocking the orifice in the restrictor valve.

In November 2007, it was revealed that the Swedish Civil Aviation Administration had begun an investigation and found Scandinavian Airlines System culpable of cutting corners in its maintenance department.

The plane reported a technical problem shortly after takeoff and was diverted to Belfast International Airport, where it landed on its nose with the front gear retracted.

In beta, which is intended for ground operations and slowing the aircraft after landing, the variable-pitch props transition to flat pitch.

[69] The Papua New Guinea Accident Investigation Commission (AIC) found that the pilots made several other serious errors, including failing to lower the landing gear and flaps, which would have slowed the aircraft and reduced the severity of the crash; however, the AIC primarily attributed the accident to the fact that it was possible to actuate beta in flight, coupled with inadequate training for flight crews to recognize and correct this situation.

[69] On December 6, 2011, QantasLink Dash 8-315 VH-SBV, on a scheduled passenger flight to Weipa Airport, encountered turbulence while the first officer's hand was resting on the power levers.

[107] While investigating these events, the AIC and the Australian Transport Safety Bureau (ATSB) determined that a number of similar inadvertent in-flight beta actuations had occurred in the Dash 8, and recommended steps be taken to prevent it, including more thorough pilot training.

[69][107] In 2012, in cooperation with the AIC and ATSB, Transport Canada issued an airworthiness directive (AD) mandating the installation of beta lockout on all Dash 8 aircraft that did not have it, a second AD mandating more frequent testing of the beta warning horn, and a service bulletin requiring a cockpit placard to warn pilots not to move the power levers below the flight idle setting while airborne.