Helping airports design taxiways to accommodate the Bombardier Q400

Bombardier’s Q400 and Q400NextGen─the newest versions of the “Dash 8”—are popular with airlines that operate in the twin engine, medium range turbo-prop market. These versatile aircraft have an 80 passenger capacity and are popular with small, in-city airports with “short” runways where regional jets often cannot operate. Moreover, the Q400 uses less fuel than a comparable jet aircraft, and is quieter and faster than previous versions of the well-regarded Dash 8.

With all these positive features, the Q400 can still pose a particular challenge for airport designers; one that is still being wrestled with by regulatory agencies. The unique placement of the aircraft’s main gear translates into a wider wheel base that theoretically increases the width of taxiways on which this aircraft operates.   

With most commercial passenger aircraft, the landing gear is placed beneath the fuselage. The Q400, as with previous versions of the Dash 8, instead places the landing gear further out on the wings, beneath the engine nacelles. This means that the Q400’s main gear width of 31 feet (9.5m) is actually wider than larger jet aircraft such as the Boeing 757 or an Airbus A320.

The Bombardier Q400 vs. Taxiway regulations

The Federal Aviation Administration (FAA) and Transport Canada’s recent revisions to their respective design guidelines changed the criteria for taxiway design. Previously, taxiway design mirrored runway design and was based on aircraft approach speeds, wingspan, and tail heights. The aircraft’s undercarriage dimensions were not taken into account.

The new versions of FAA AC 150/5300-13A and Transport Canada’s TP 312 5th edition create taxiway design guidelines that now take an aircraft’s main gear width into consideration.  Transport Canada’s TP 312 classifies the Q400 as an Aircraft Group Number IV in a taxiway environment. This would require a Q400 to use taxiways with a minimum width of 75 ft (23m).  The requirement is at odds with the current width of the taxiways in many smaller airports, particularly in Canada, where the Q400 operates. Meanwhile, the FAA currently does not characterize the Q400, as it falls outside any of its Taxiway Design Groups (TDGs).

I reached out to Bombardier on this issue and they point to the Q400’s short cockpit to main gear length, narrow body and low ground stance, all of which provide the pilot with exceptional pilot eye to taxiway edge view. Indeed, Bombardier operated the Q400 safely on 50-foot (15m) taxiways during their flight test program—narrower than Transport Canada current guidance.

Airport design considerations for the Bombardier Q400

Airport engineers designing taxiways where Q400 may be present should be aware that although there may be much larger aircraft operating at the airport, the Q400 will often be amongst the most demanding aircraft for taxiway design. Here are several suggestions for airport operators, airport designers and regulatory agencies to consider:

• Factor the unique attributes of the Q400 aircraft into future airport master planning
• New, or clarified, guidance from the FAA and Transport Canada on taxiway dimensions may be warranted. In particular, the FAA should consider characterizing the Q400 within its TDGs
• Consider whether or not these taxiway requirements, as applied to the Q400, are truly integral to the safe operation of this aircraft.