Our indicated airspeed on final approach was an astonishing 64 knots. That’s quite slow in any airplane, but it seemed genuinely surreal when I turned around in the cockpit to confirm that I was indeed flying a 19-seat turboprop commuter. Moments later, I pulled the throttles to idle and settled Viking Air’s Series 400 Twin Otter onto Runway 09 in Victoria, B.C. A decisive application of brakes and reverse thrust, aided by a 10 knot headwind, brought our light aircraft to a stop in around 1,200 feet. Reconfigured for takeoff, I released the brakes and was again airborne in the time it takes to form a broad grin.
There is indeed something special about the Twin Otter.
The flight manual specifies that the aircraft can land in 1,510 feet and take off over a 50-foot obstacle in 1,490 feet at maximum weight, under sea level standard conditions with no wind. That is truly impressive field performance for this class of aircraft, and it is a big reason why the Twin Otter is enjoying a successful renaissance, thanks to Viking’s initiative.
While it was developing the modern Twin Otter, Viking formed a technical steering committee to get operator input into its design. Several features from the legacy aircraft were subsequently carried over to the Series 400.
Viking invited Skies magazine to test fly Twin Otter serial number 889, the 45th Viking-built Series 400 aircraft. Flying over the green hills west of Victoria, production pilot Chris Denko supervised as I put this factory-new Twin Otter through its paces. Steep turns, slow flight and stalls could only be described as easy. The Series 400 flew exactly like, dare I say, a Twin Otter. It has a steady, stable, predictable feel, and it presents no unexpected challenges to the pilot. Agile, nimble, responsive…no, those aren’t words that leap to mind about the Twin Otter’s handling qualities, but one quickly grasps the impressive capability of the machine.
The slow speed regime is where the Twin Otter really shines. The published stalling speed with the flaps retracted at maximum gross weight is only 73 knots indicated airspeed (KIAS), but deploying the generous, full-span, double-slotted Fowler flaps to their full 37.5 degree extension reduces the stalling speed to an impressive 56 KIAS. That equates to a 23 per cent flap-induced decease in stall speed. Find another airplane that does that! Those are powerful flaps, and they define much of the unique “personality” of the Twin Otter.
The worldwide fleet of new Series 400 Twin Otters boasts the full spectrum of landing gear options – straight and amphibious floats, wheel skis, intermediate flotation gear, and standard fixed wheel gear.
Those big flaps produce tons of lift, but there’s no escaping the fact that they likewise create considerable additional drag. I wanted to see if all that drag in the landing configuration could get the pilot into trouble. The worst case scenario would be an engine failure during a balked landing at low altitude. For safety’s sake, we simulated it at a safe height. At 6,000 feet, Denko and I configured the aircraft for landing with 37 degrees flap and commenced a descent to an imaginary airport at 5,000 feet, using the published approach speed of 64 knots. Just as we were about to touch down, I convincingly imagined that a moose bounded onto the runway and commenced a balked landing. By prearrangement, our left engine also suddenly “failed,” and I was left to contend with a single-engine overshoot with full flaps.
With the exception of composite panels in selected places, Viking’s Twin Otter employs the same construction as the legacy versions, including the well proven PT6A-34 engines.
The sudden burst of asymmetric thrust at our low speed required full rudder and a decisive application of opposite aileron; 64 knots coincidentally also being our minimum control speed (Vmca). Arresting our rate of descent left us floating for a few moments at a precarious airspeed, while Denko simulated the function of the autofeather system, following which the airspeed began to climb, and shortly thereafter so did the Twin Otter. Conducting this test well below maximum gross weight was far from a worst case scenario; however, the verdict was that although the balked landing was a bit technique intensive, the Twin Otter is not so “muscle bound” by its powerful flaps that it can fly itself into any dangerous corners.
Flying slowly isn’t typically associated with safety, but I was unable to find any rough spots in the Twin Otter’s handling. We did stalls clean and with full flap, with the power at idle and at low-cruise setting (25 psi engine torque). Admittedly, our light weight and forward centre of gravity showed its best side, but the stalls we performed were all aerodynamically benign. With the requisite warning lights and auditory cues (“Stall! Stall!”) I couldn’t have missed it had I been sleeping. Throughout its flight envelope, I found the Twin Otter’s handling exceptionally friendly and forgiving.
Ostensibly to assess cruise performance, but in fact to do a few minutes of surreptitious sightseeing, I set course at 5,500 feet along the rugged west coast of Vancouver Island. Configured as a commuter, with a crew of two, our aircraft had a basic operating weight of 8,118 pounds. With 1,800 pounds of fuel onboard our gross weight was roughly 9,900 pounds; well below the 12,500 pound maximum takeoff weight. Had we filled the tanks to the 2,576 pound standard capacity (not including the optional tip tanks), the residual payload would have allowed for nine standard-sized passengers.
Setting a high-speed cruise power setting of 48.5 psi torque on each engine, the speed settled at 149 KIAS, equating to 162 knots true airspeed. At an outside air temperature of 16C, the engine temperatures (T5 of 669C and 659C respectively) showed a generous margin below the 765C maximum continuous rating. Clearly, the well proven PT6A-34 engine could sustain the 585 HP maximum continuous power rating up to much higher or hotter conditions. The engine’s 620 shaft horsepower takeoff power rating is available to +27C. Our high-speed cruise test was hardly miserly, however, demanding a total fuel flow of 668 pounds per hour.
To demonstrate performance where range or economy were more of a priority, Denko selected 37.2 psi torque on each engine and allowed the Twin Otter to settle into a leisurely cruise at 150 knots true airspeed. Fuel flow dropped to 539 pounds per hour. Viking Air claims that the direct operating cost for the Series 400 is US$814.73 per hour.
Customer training is provided by Viking subsidiary Pacific Sky Aviation, and is tailored to individual requirements. Denko mentioned that most customers have prior Twin Otter experience, so the check-out is often limited to differences training. The addition of a Level D simulator and associated training facilities currently planned for construction in Victoria will enhance Viking’s training capabilities.
Throughout its flight envelope, Erdos found the Twin Otter’s handling exceptionally friendly and forgiving.
WORKING IN A GLASS OFFICE
Upon completion of our sightseeing, um…performance tests, we returned for a GPS approach to Victoria’s Runway 09. Denko demonstrated the set-up of the flight management system (FMS). The addition of a Honeywell Primus Apex avionics suite changes the personality of the Twin Otter from a 1960s artifact to a thoroughly modern airplane. The Apex system is optimized for single-pilot operation, and seemed well suited to the Twin Otter. Although I mainly observed as Denko did the button poking, I found the tab format of the screens very easy to interpret. Navigating the separate data panes on each screen with a cursor seemed a logical interface. The placement of the FMS keyboard on the centre of the Y-shaped yoke had the bemusing effect of causing the keyboard to move whenever I made elevator inputs. The devil on my shoulder whispered in my ear, and I couldn’t resist jiggling the elevators as Denko commenced typing, causing him to momentarily chase the keyboard—all without as much as a scowl. Demonstration pilots are so polite!
From my perspective, the big surprise with the Series 400 avionics was the absence of an autopilot. What?! It’s broken? No, absent. Not yet available. They had to tell me twice before I would believe that an EFIS-equipped 19-passenger commuter transport could be marketed without an autopilot. To be fair, Viking and Honeywell are currently performing certification testing on the autopilot and flight director, which are expected to be available by autumn 2014. Denko advised that the system should easily retrofit into existing Series 400 aircraft. Pardon my glass-half-full attitude, but I think it speaks volumes for the market demand for the Twin Otter that the absence of an autopilot from such an otherwise capable avionics system has hardly dampened customer enthusiasm. Viking’s marketing associate, Angie Murray, offered that the company gauged market demand for the Series 400 sufficiently strong to support a phased approach to certification, with the initial goal of quickly getting the aircraft into customers’ hands. Certification of further equipment and options will follow.
The new Twin Otter performs a variety of civilian and military missions. It serves as a regional commuter, a parachute platform, a corporate shuttle and a training/charter aircraft, as well as a personal VIP transport.
Certain quirks, such as a “Mach” option when inputting cruise performance data, are indicative of the maturation process of the Apex system in the Twin Otter, and betray its origins in “biz jet” avionics. Excuse my curmudgeonly my curmudgeonly nature, but I’m often skeptical whether modern fancy glass cockpits aren’t sometimes a bit too smart. Indeed, the Apex system was at times a distraction, with a series of annoying beeps, bings, bongs and voices, especially during start-up. In flight, the enhanced ground proximity warning system (EGPWS) persistently tried to save our lives as we attempted to enjoy some contour flying during a photographic diversion over Cowichan Lake. In fact, the system was persistent any time we descended below 500 feet in the absence of a database-defined aerodrome. This seemed odd in an airplane that excels in operating from unprepared locations.
With a typical instrument approach speed of 90 knots, I was concerned whether the Twin Otter would fit into the traffic flow at busier airports. Denko offered a demonstration, wherein we flew the GPS approach at 150 knots with the flaps retracted, and then at three miles from the approach minima we hauled back on the throttles to hasten the deceleration to the 103 knot flap extension speed. There can be no doubt that the Twin Otter has plenty of drag when you need it, and we were comfortably established at our prescribed approach speed within a half mile. Point made.
The Honeywell Primus Apex avionics suite changes the personality of the Twin Otter from a 1960s artifact to a thoroughly modern airplane.
VERSATILITY IS STILL IN DEMAND
The story of the Twin Otter today is the same as it was when the design emerged from the drawing board in 1964. Viking claims their customers told them that the only replacement for their fleet of stalwart old Twin Otters would be brand new Twin Otters. Viking listened.
There are faster turboprop twins, but customers buy a Twin Otter because it does things that other airplanes simply can’t do. There are some rugged and inhospitable regions on our Earth, and pilots flying conventional runway-bound people-movers would naturally consider those areas inaccessible. Snowy Arctic tundra, remote lakes, mining strips deep in the bush…the Twin Otter changes the equation from having nowhere to land to suddenly having everywhere to land. Viking’s Series 400 Twin Otter is an airplane that will take you places.
Robert Erdos is a contributing editor for Skies magazine. He is a professional test pilot with over 8,000 hours of flying experience on a wide variety of aircraft. A graduate of the US Navy Test Pilot School, he is a former RCAF test pilot who now works as an Experimental Test Pilot for the National Research Council in Ottawa. In his spare time, he does formation and airshow aerobatic flying as a pilot for Vintage Wings of Canada.