While seldom remembered following the launch of its highly successful younger brother, the Dash 7 is an aircraft we cannot forget as it truly did bring the concept of STOL aviation to the masses, and was the linchpin of many important airlines and their regional operations.
Prior to the Dash 7, de Havilland Canada had already cemented its reputation as a provider of sturdy and reliable STOL (Short Take-Off and Landing) aircraft, primarily through the incredibly popular DHC-6 Twin Otter. The problem with STOL aircraft of the time however was the fact that they were too small to make much of an impact on commercial aviation. The DHC-6 was great at working low capacity routes in the Caribbean or in the snowy mountains of Alaska, but for higher capacity routes to regional airports in Europe and the United States, the frequency would’ve made such operations cost prohibitive. The idea of larger STOL aircraft wasn’t a new one though, as by the end of the 1960’s there were a slew of Turboprop designs that could land on comparatively short runways, namely the Fokker F27, and it’s license built American cousin the Fairchild F-27, the Convair 580 and 600, and Hawker Siddeley 748.
The market de Havilland hoped to sneak into was for city centre airports, small fields with no room to expand due to urban growth, but, due to their proximity to the Central Business District, were in high demand. de Havilland also wanted a STOL aircraft that was sturdy enough to land on uneven runways, such as those comprised of gravel, or were improvised. Initial designs called for a 40-passenger aircraft with a 200 mile range that could operate from runways as short as 2,000ft.
However, upon entering the 1970’s, new legislation regarding noise meant that aircraft were restricted to a certain decibel level, especially on routes to city centre airport. This was factored in by de Havilland, who created a new design for much larger (oversized) propellers geared to rotate at a slower speed than is normally designed. Much of the problem sound from a typical propeller is generated at the tips of the blades which are rotating just beneath the speed of sound. By using overlarge propeller blades there is no need to have the blade tip reach near the speed of sound, and the RPM can therefore be reduced without sacrificing thrust. In reducing the RPM this noise is reduced substantially. The propellers on the Dash-7 are constant speed propellers which change the blade angle to push more or less air as needed. This can be used to change power while maintaining a constant (and lower) RPM.
In essence, the overall design of the Dash 7 (a.k.a DHC-7) was identical to that of the DHC-6, being only larger and fitted with four engines. The design included a high-mounted wing, cockpit configuration and nose design. However, this is where a majority of the similarities end, with changes to the design including the addition of cabin pressurization (requiring a switch to a fuselage with a circular cross-section), landing gear that folded forward into the inner engine nacelles and a large T-tail intended to keep the elevator clear of the propwash during takeoff.
The key to the Dash 7’s success as a STOL aircraft of larger proportions came down to the aileron configuration. In comparison to the DHC-6, the -7 had reduced size ailerons to
allow for more flap area, and were augmented with two sets of roll spoilers. The inboard roll spoilers operate at all speeds while the outboard roll spoilers only operate at speeds less than 130 knots, allowing for more roll control at slower speeds. Upon touchdown, both the inboard and outboard roll spoilers extend in unison to aid in removing lift created by the wing. Each wing also includes two ground spoilers which only extend on touchdown. Most of the trailing edge is spanned by a complex double Fowler flap arrangement for high lift at low speed.
During a typical STOL landing, flaps are selected to the 45° position, generating more lift and drag and thus allowing for steeper descents and slower approach speeds. Depending on weight, the VREF speed with flaps at 45° is between 70-85 knots. On touchdown, through “squat switches” in the main gear, the flaps automatically retract to the 25° position and thus reduce lift once on the runway producing better braking performance. The flaps also retract to 25° when engine power is increased during a go-around procedure. The four-engine layout aids lift at low speeds due to the wide span of the propellers blowing air over the wing (“propwash”). When reverse thrust is selected on landing, the props reverse pitch, push air forward and slow the aircraft very effectively along with the anti-skid wheel brakes. More importantly, if an engine fails, the asymmetric thrust is much less than on a twin-engine layout, thereby increasing safety and allowing for a lower VMC (minimum control speed) with an engine inoperative.
The Dash 7 project was officially launched in 1972, with the first flight being performed on March 27th, 1975. The maiden flight was followed by extensive testing in some of the harshest conditions imaginable, mostly under the supervision of launch customer Rocky Mountain Airways. The Dash 7 was flown in snow, driving rain, high winds, on runways that barely existed such as grass strips, rocky gravel and icy tundra. But eventually, after its exhaustive trials, the first aircraft was delivered to Rocky Mountain Airways on February 3rd, 1978. The first commercial operations of the -7 were on flights from Denver to the Avon STOLport in Colorado, located in a mountain valley near the popular Vail ski resort.
Very quickly, the -7 garnered a reputation based on its incredible STOL abilities, a perfect mixture of performance and capacity. As such, airlines and airport developers rapidly saw its many benefits, and created airports specifically designed to take the Dash-7. Perhaps the most notable airport to be based entirely with the Dash-7 in mind was London City Airport in the London Docklands. During the 1970’s and 1980’s, connections to London’s 5 international airports, Heathrow, Stansted, Gatwick, Southend and Luton, were not their best, with journey times of up to and over an hour between the city’s many stations and the terminal. In 1981 however, London Docklands Development
Corporation (LDDC), the company overseeing the regeneration of the largely redundant London Docklands, felt that a major incentive for large scale economic growth in this region was the addition of an international airport, complimented by the proposed Docklands Light Railway. While many doubted the feasibility of such a scheme, investors were curious as to the idea, especially since the concept of the STOL aircraft had now been expanded upon by the Dash 7.
As a proof of concept, June 27th, 1982, saw Captain Harry Gee of Brymon Airways, a UK-based regional airline and one of the main backers of the project, land a Dash 7 on Heron Quays, in the nearby West India Docks. This was followed by a full LDDC feasibility study, which resulted in an opinion poll by local residents almost unanimously in favour of the airport’s construction. By 1983, Planning Permission was granted, and the airport was eventually opened in 1987. The airport’s first airline, London City Airways (a subsidiary of British Midland), made its first flights to the near continent using the same aircraft that had started it all, the Dash 7. Since then, that, and the opening of the Docklands Light Railway in 1987, has seen what was once the redundant dockyards of east London transformed into one of the largest and most influential financial centres in the world, with international connections only minutes away at City Airport.
Eventually, 100 Dash 7’s were constructed when mass production of the aircraft ended in 1984, following the launch of the aircraft’s successor, the Dash 8. However, 13 occasional orders were delivered until 1988 when the aircraft was removed from the product list, the last example being bought by Tyrolean Airways. A majority of the aircraft sold were the DHC-7-100 originals, which was divided into two sub-models, the -102 passenger and the -103 combi-freight, distinguishable by its large cargo door. This was followed by the DHC-7-110 and the DHC-7-150, which included additional fuel tanks and an improved interior. Plans for the DHC-7-200 with new PT6A-50/7 engines, allowing for operations from hot and high airports such as Nairobi in Kenya, were scrapped when Boeing bought de Havilland in 1986 and ended production of the type.
The Dash 7 also gained a number of military orders. The first of these was for two aircraft for the Canadian Armed Forces, who needed them to transport high ranking passengers and freight around Europe. These aircraft received the CF designation CC-132 and were delivered to 412 Transport Squadron at Canadian Forces Base Lahr, in West Germany. The United States Army also operates several Dash 7 aircraft as surveillance platforms with the designation EO-5C (RC-7B before 2004) under the Airborne Reconnaissance Low program.
Transport Canada operates a single DHC-7-150IR aircraft to conduct maritime surveillance, pollution and ice patrols as part of the Transport Canada National Aerial
Surveillance Program (N.A.S.P.). The aircraft’s home base is Ottawa, Ontario, Canada. During the summer months this aircraft conducts patrols throughout the Canadian Arctic, Alaska and Greenland. During the autumn and winter months this aircraft conducts patrols of the Great Lakes and east or west coasts of Canada as required.
Plans were also made to evolve the aircraft into a more conventional twin-engine design in 1978, this eventually forming the basis of the incredibly popular Dash 8. In total, 113 aircraft were delivered, and managed to make their way into a slew of very important airlines, including Brymon Airways, Wardair, Air Greenland, Tyrolean Airways, Hawaiian Airlines, Trans World Express and USAir.
However, the Dash 7 has sadly not been immune to tragedy, as even this plucky little airliner has lost family members. The de Havilland Canada DHC-7 has been involved in six accidents (and 10 incidents overall) with a total of 68 fatalities.
The first loss of a Dash 7 took place on May 9th, 1982, when an Alyemda DHC-7-103 crashed into sea near Aden International Airport in Yemen killing 23 of 49 on board.
The worst incident however was on May 6th, 1988, involving Widerøe Flight 710. This aircraft crashed into a hillside during poor weather near Brønnøysund Airport in Norway, killing 36 on board, the cause later being determined to be due to several shortcomings in the airline’s operating procedures, in particular lack of proper cockpit communication and mutual control of the descent and approach plans. This was in part caused by the airline electing to not follow the Sterile Cockpit Rule and that a passenger was sitting in a cockpit jump seat during the flight. The investigating commission also found lack of proper pilot training in the airline. Flight 710 was the second of four Widerøe accidents between 1982 and 1993, all of which revealed shortcomings in the airline’s operations and internal control.
The latest incident involving the Dash 7 was on May 1st, 2006, when a Trans Capital Air, working for United Nations Mission in Liberia (UNMIL), aircraft crash landed at Zwedru Airport in Liberia after landing gear failed to extend, but thankfully with no injuries among its 40 passengers.
Today, most Dash 7’s have long since been superseded by the highly popular Dash 8. Most major airlines saw off the last of their members by the end of the 1990’s, and while some have found themselves an active life with other smaller airlines or working for government institutes, the remainder have either been stored or scrapped. As of 02/2017, there are 47 Dash 7’s still known to be in operation across the world, mostly in the skies above its Canadian home.
As mentioned, the Dash 7 is an aircraft frequently forgotten, pushed into obscurity by the Dash 8 that replaced it, which I feel is the saddest part. The Dash 7 is a wonderful aircraft, strong, reliable, endearing, chocked full of performance and generally just a good egg all around. The worst part is that many don’t really consider the -7 a classic like they do early versions of the -8, or even the preceding DHC-6, it instead being seen as just a bridge between the small Twin Otter and the larger Dash 8. But personally, I think it’s a perfect contender for a classic airliner, an aircraft that brought the airport into the city, and got rid of those pesky commutes that usually take longer than the actual flight!