Airtest-Pilatus Britten-Norman Islander

Our 20 minute flight crossed terrain that, using the best alternative transport, would have taken us an entire bruising, dust choked day. Our lake edge destination was a red brown dirt airstrip roughly hewn from the bush, irregularly bordered by termite mounds, and guarded by a small herd of watchful elephants. The pilot skillfully dropped us onto its very threshold and I watched, fascinated, as the rugged machine’s long undercarriage legs vibrated fore and aft under the pounding from the rough surface.

I was amazed to see that this was merely a scree of crushed rock lumps up to the size of my fist; they were flung up behind us as we juddered to a halt. Now I realized the purpose of the black rubber strips on the tailplanes. Not deicing boots, they were simply locally devised protection against the pummelling from those miniature boulders! In that brief flight I began to realize just how tough and capable this indomitable little workhorse is, and why it has been a success for so long, especially in the World’s more remote regions. There are 22 in Australia to date, with six more soon to arrive.

Having first flown in June 1965, the economical and versatile Islander is a full 30 years old this year. Pre dating the Concorde, it is now nearly a hundred times more successful; over 1200 units having amassed a total of ten million hours in 120 countries, making it Europe’s best selling commercial aircraft. This is a remarkable and rare British aviation success story, and completed airframes continue to leave Pilatus Britten-Norman’s Bembridge factory at the rate of two to three per month. Even now, since it has no specific fatigue life, the Islander’s main competition is not any more modern or sophisticated commuter plane, but a used example. One in Fiji has logged a staggering 28,000 hours and is still going strong.

The perennial Islander was the brainchild of gifted ex de Havilland aeronautical engineers Desmond Norman and the late John Britten. They designed the aircraft so well it has changed little since its debut. The original 210 horsepower (155kW) Continental engines were soon replaced by stronger and more reliable Lycomings, the beefed up airframe grew a couple more feet of wing span, and its maximum weight rose to 2993kg (and can be increased to 3150kg for ferry flights). Worldwide experience resulted in a few refinements, including improved ventilation, better door locks, sills and seals and shorter propellers to reduce noise.

A modern interior is now finished in lightweight but tough, light grey, easily cleaned or replaced, vacuum formed polycarbonate panels with sound proofing bags behind them. These better meet the UK CAA’s latest fire worthiness requirements than the former fabric covered ply sheets and are more tolerant of temperature extremes. They incorporate integral ashtrays, individual air vents, lights, inertia reel shoulder harnesses, speakers and air conditioning outlets.

From the base model BN2B-26 with its pair of 260 horsepower (195kW) Lycoming O-540s, the family has expanded to include the higher performance, fuel injected, 300hp (225kW) BN2B-20, the heavier (but quieter) 320shp (240kW) (derated from 420shp 315kW) Allison turbine engined BN2T and a whole range of turbine engined military Defenders. These include several with odd noses for a variety of surveillance radars. An unconventional early development was the three engined, 18 seat Trislander, of which 90 were built for commuter operators. There has recently been some demand from those companies still using the type (especially in the Far East) to recommence building this finite lifed airframe. The Bembridge team has developed a Trislander relifeing and refurbishment programme, and could reopen the production line, but may not be able to persuade their Swiss masters to approve.

I have read that Britten-Norman’s pilots used to demonstrate a takeoff on one engine alone, even then only using a ground roll of little more than 700 metres.

Bembridge’s latest product is the new, bigger, four tonne BN2T-4S Defender 4000, using the Trislander wing, fuselage centre section and undercarriage, and powered by two 400shp (300kW) Allisons. Its revamped airframe incorporates numerous improvements, including stronger hard points, a sliding door, a deeper windscreen, more powerful 200 amp generators, modern avionics including EFIS and GPS, and a longer nose capable of carrying bigger 360 degree radars. Increased internal fuel and a higher takeoff weight give it a one tonne full fuel maximum payload and an endurance of nearly eight hours.

In 1972, after financial problems, the Islander line was sold to Avions Fairey of Belgium, to be rescued in turn by Oerlikon Bührle’s subsidiary, Pilatus, in 1979. Under this Swiss administration, basic airframes continue to be built using lower cost labour by IAv Bucuresti in Romania, but development, testing and final assembly still take place on the Isle of Wight where PBN enjoys reasonable autonomy. Their pilots fly bare ‘green’ primer painted airframes the ten and a half hours across Europe using one of three pairs of dedicated part life engines and comprehensive radio ferry packs. At Bembridge the aircraft get new zero hour engines and are completed with their customers’ options, avionics, interior and paint scheme before delivery.

It was here that I was introduced to the marque in more detail by PBN’s Chief Test Pilot, John Ayers, ETPS graduate, former Tiger Club display pilot and one of the UK’s four current seaplane rating examiners. Showing me around the ten near complete airframes in the final assembly hangar, he indicated the family’s salient features, concentrating on the 260 horsepower (195kW) BN2B-26 version we were to fly.

Its 14.94 metre span, constant chord, two spar wing has no dihedral, uses the universal NACA 23012 section for good CofG tolerance and has half span electrically powered slotted flaps. With settings of 25 degrees for takeoff and 56 degrees for landing, these do not quite fully retract but hit fixed up stops at six degrees, the established minimum drag position. Such were Britten’s and Norman’s skills as designers that, apart from a small area of fixed droop inboard of the engines, there are no sophisticated high lift devices. Yet this apparently simple wing confers true STOL performance, heaving a 3000kg aircraft over a 15 metre obstacle in under 300 metres on a calm standard day. John attributes this partly to its ‘built in vortex generators’, a row of half centimetre thick oval inspection panels spread along the upper surface and clearly visible from above in my accompanying photographs. Each wing carries an integral 259 litre fuel tank whose sumps protrude beneath its underside, while an optional pair of fibreglass wing tip tanks will boost total capacity to 855 litres.

Asymmetric loads are minimised by mounting the engines close to the fuselage, but they are a little high for easy preflight inspection. While the right one’s dip stick can be checked by standing on the adjacent door sill, the left nacelle can only be reached using the refueller’s ladder. The strong, wide track, fixed main undercarriage legs are mounted aft of the rear spar and survived an impressive ten foot per-second drop test in the Bembridge hangar. The twin main wheels have low pressure tyres for use from unprepared grass, gravel, shingle or beaches, but make it difficult to land the aeroplane consistently gently. The nose leg is bolted to the front bulkhead and the pointed cone ahead of it conceals the avionics. An optional elongated, baggage carrying version is available.

Sitting just 57cm off the ground for easy entry and loading, the boxy fuselage’s small, 1.09m by 1.27m cross section creates minimum drag, and yet seats ten adults in pairs in fair comfort. Up to 180kg of luggage can be carried under an integral flexible plastic screen in the 1.39cu m aft baggage compartment, or all four benches can be removed in a couple of minutes to permit the full 4.7cu metre cabin to be fitted with three stretchers or filled with up to 900kg of freight over short stages. The heater unit and optional air conditioner occupy the rear fuselage, with inlets near the compass remote sensor at the fin’s base. Intakes for the ventilation louvres are in the inboard leading edges. There is a fixed tailplane, and both rudder and one elevator carry manual trim tabs (there is no electric trim option). The tail bumper incorporates a tie down point.

The left passenger and cargo doors open to latch well aft of the wing, while the right door is just ahead of it, but hinges out to a catch on the nacelle to keep passengers safely behind the engine. Microswitches on the passenger doors feed a cockpit warning light (best checked by the pilot before he buckles up and starts the engines). His forward door also latches open, this time with an over long catch which frequently cuts the rubber sealing strip and should have been improved long ago. This door has a big foot square clear view panel. It is locked by an (overrideable) electro mechanical bolt connected to the left engine’s magneto switches to prevent the pilot jumping out into the rotating propeller. A large composite panel bonded to the right door protects it from ice shed by the prop. (The left engine tends to throw ice outwards, away from the fuselage). Pneumatic wing, fin and tailplane deicing boots and electric propeller deicing are optional.

Standard cockpit equipment includes dual controls, a single set of normal flight instruments, twin nav/coms with glideslope, marker receiver, ADF, DME and transponder. Options embrace an autopilot, weather radar, HF radio, RNAV, VLF/Omega or GPS supplementary navigation equipment. All are set in big light grey instrument panels divided by twin stacks of small engine gauges (for standardisation with the turbine Islander). Below these a neat power quadrant also holds the elevator trim wheel and indicator, with the flap switch, carb heat levers and park brake on its aft face. Most switches for the 24 volt electrics are mounted on the left lower sub panel, while the right one carries the circuit breakers. To the left of the upper engine instruments is an eight light annunciator, and our simply equipped example had just an ASI and altimeter on the right.

An eyebrow panel above the windscreens carries fuel gauges and pumps, starter and magneto switches, flap position lights and volt/ammeter. In the pilot’s upper screen are the OAT gauge and standby compass, while the rudder trim and simple, red and green, three position (off, left and right) fuel selectors live in the roof. Cabin air and temperature controls are above the left door pillar. This cockpit seems a bright and airy workplace and, although it is not overly roomy, everything is within easy reach. Although its twin seats are fixed well away from the panel, their position is comfortable, and the rudder pedals can be adjusted over a reasonable range.

Both carburettor equipped Lycomings started instantly and without fuss, both from cold and later, once they were hot; a useful characteristic for the type’s usual quick turnarounds. Releasing the parking brake revealed good, although moderately heavy, nose wheel steering through a 20° angle. Full lock plus differential power and brake disengages the linkage, allowing the wheel to castor at nearly ninety degrees so the aircraft will pivot around its stationary inner main wheel for a 9.45 metre turning circle. But I had trouble keeping my feet well clear of the brake pedals, which I found only too easy to press in error. Although these new units worked well, the Islander’s brakes are not reckoned to be its most reliable system.

For our flight John quickly acceded to my request that the aircraft be representatively heavy, and within minutes the seats had been removed and replaced by ballast boxes putting us at maximum takeoff weight. With standard tanks carrying 518 litres of fuel (weighing 372kg) a 670 kilo load was available; enough to take seven passengers and 50kg of baggage. Alternatively, filling all ten seats would have enabled us to carry 373 litres of fuel, for a three hour empty tanks endurance or a 350nm (650km) VFR range.

I had the benefit of a strong crosswind for most of my flights, and this one was no exception, with a gusting 15 knot southerly blowing at right angles to the runway. John cautioned that the Islander’s high wing needs lots of into wind aileron, so I cranked the yoke well over with my left hand as I unleashed the raucous Lycomings with my right. Despite our considerable mass, we reached 35 knots in no time, and I eased back on the yoke to unstick at 50.

Takeoff safety speed is 55kt (102km/h), and both blue line and best rate climb speed are 65 knots, but I allowed the eager machine to accelerate to 90 (167km/h), which is more normally used for passenger comfort and adequate engine cooling. Passing 200ft and with 100kt (185km/h) on the clock I retracted the flaps, discovering in the process that the switch has to be held in the up position for a full second to latch in. Retraction induced some sink and a nose down trim change, after which I could throttle back to the climb power of 24 inches manifold pressure and 2400rpm, reducing the noise to an acceptable and reassuring drone.

At first I found it a little hard to interpret the small engine gauges, but doubtless this would come with practice. I also discovered that the rudder has to be properly in trim for the best climb performance, which got us to 5000 feet in less than ten minutes from brake release.

The aeroplane has the stability, ease of control and feel of a bigger aircraft. As John said “It is basically very easy to fly, but to get it to operate efficiently you have to work at it.” This benign character is ideal for the low hour pilots who will often be flying it. Leaving the manifold pressure at 24 inches and reducing revs to 2250rpm, as briefed, I carefully eased the mixture levers back exactly to the bottom of the X in the word mixture on the quadrant. This gave us an IAS of 124kt (230km/h) which, at 5000 feet and in near ISA conditions, equated to 133kt (245km/h) TAS, not bad considering the fixed undercarriage and boxy shape. Normal fuel consumption is around 100lph for a range of up to 675nm (1250km) with VFR reserves. Islanders have never been known for their internal quietness, but removing my headset for a few minutes proved that occupants can talk to each other over the engines’ din, provided they raise their voices.

Despite the cockpit’s position well ahead of the leading edge, like many other commercial aircraft the Islander has a rather shallow windscreen so, while the downward view is excellent in turns, visibility towards the inner wingtip is only adequate. (The Defender 4000’s improved windscreen extends further aft, but it will probably be too difficult to fit this to the Islander family.) With little visible nose ahead for pitch reference, at first I found it hard to maintain height accurately, but even full aileron rolling into and out of 45 degree banked turns became easier with practice. John assured me “controllability is excellent for surveillance work, although it does need a hefty heave on the wheel to fly level at sixty degrees of bank”.

Increasing rpm, enriching the mixture and checking the very effective carb heat, we completed our HASELL checks and, as we slowed to sample the stall, I trimmed against the big nose down pitch change with reduction of both power and speed. Without flaps the reedy high pitched warning horn sounded at 57kt (106km/h). Some sink developed during the one knot per second deceleration, followed by light airframe buffet and an almost immediate break at 49 knots (91km/h) with the nose twelve degrees above the horizon and considerable stick load. Because I held the wheel back, we suffered a fair right wing drop. On my next attempt, with a slightly quicker speed reduction and immediate release of the back pressure at the stall, we broke straight ahead at 48kt (89km/h). The Islander’s common NACA 23012 aerofoil never gives much aerodynamic warning at high wing loadings and always tends to quit flying abruptly, so this behaviour was to be expected.

The bright and airy cockpit’s standard equipment includes dual controls, normal flight instruments and airways avionics. All are set in big light grey panels divided by twin stacks of small engine gauges (for standardisation with the turbine Islander).

Selecting takeoff flap caused a significant pitch up and heave, which is quite controllable provided you anticipate it. This reduced the stall speed to 44kt (82km/h) at about ten degrees nose up in noticeable sink and with full back stick after the horn had bleated its warning at 53kt (98km/h) IAS. Again I held the aircraft in the stall for a little too long, this time getting a left wing drop. Full flap required a good pull to keep the speed reducing, and I saw 700ft/min on the VSI before the 43kt (80km/h) stall. Recovery was prompt in each case on releasing the back pressure and applying power.

Throttling back the left (critical) engine at 65 knots from a full throttle, maximum rpm, takeoff configuration climb induced an easily controlled swing as I quickly lowered the nose to hold our speed. Maintaining wings level with the slip ball centred we suffered a slight height loss before I could feather the propeller and retract the flaps. Thereafter, with four or five degrees of right bank and the ball displaced half its width for maximum performance, I was just able to hold height at its single engine ceiling of 5000 feet. The rudder load was not unreasonable, and easily trimmed out.

When I earlier mentioned to Bob Cole, the UK CAA’s Light Aircraft Test Pilot, that I was to fly with his former associate, he suggested I sample the Islander’s maximum weight engine out Vmca. Since he did so with his characteristic grin and twinkling eye, I was forewarned of an interesting experience. Leaving the right engine at full throttle, John reset takeoff flap and I let the speed bleed off. Below 55kt (102km/h) the rudder pressure became very heavy. With a little bank into the live engine I was able to maintain directional control right down to 42 knots (two knots below the power off stall at this flap setting) despite the pre stall buffet and incessant, wailing horn. This is an impressive capability.

Upper air work complete, it was time to go back and tackle that crosswind again. John assured me the Islander’s limit is a generous 30kt (56km/h) and, provided I used the wing-down technique with lots of into wind aileron, I should not find it a problem. Reducing power to 20 inches and 2000rpm and descending at 500ft/min for the comfort of our imaginary passengers’ ears gave us an IAS of 120kt (222km/h). Once downwind, I slowed to establish John’s recommended descending base leg at 90kt (167km/h) with approach flap and 2400rpm. On final I bled the speed back to 65kt (120km/h) with full flap for a threshold speed of 60 (111km/h). John assured me that a higher speed touchdown is feasible, the aeroplane will not bounce, and it is quite possible to fly down final at 150kt (278km/h) and land flapless to fit in with a large airport’s jets.

Closing the throttles over the threshold caused a slight pitch down, necessitating quite a heave for the flare. But, although the stick force is fairly high, it is no more than on some much lighter twins. We touched down reasonably gently and under full control on each of my attempts, but I never did manage a truly smooth touchdown.

Simulating an engine failure passing 300 feet, I found the foot force needed to stay straight was again quite high, but, once clean, the aeroplane climbed away at 150 to 200ft/min. John warned that it was more important to lower the nose quickly to catch the speed, and then to feather the failed engine’s propeller, than to retract the flaps. This nicely simple aeroplane presents no further concerns about landing gear, cowl gills or other complications, making it only necessary to retain control, maintain a positive climb, identify the failed engine and feather the prop. Even at max weight, from more than 55 knots the aircraft will gradually gain speed in ground effect to enable safe flap retraction. As usual with performance C types, if an engine should fail at below blue line speed during a very short takeoff, it may be impossible to clean up and climb in the available distance. In this case it would probably be wisest to close both throttles and accept the inevitability of a controlled straight ahead deceleration.

The single engined circuit is flown at the same speeds, but with a 300 foot decision height (partly because the aeroplane will lose at least fifty feet in the go around). Full flap is lowered at the last minute. To go around you apply full throttle, reduce speed to 65kt (120km/h) and retract the flaps to establish a climb.

When I had a feel for the aircraft, I asked John to demonstrate his forte, a short takeoff and landing from Bembridge’s tiny 230 metre grass STOL strip. Taking advantage of a ten knot headwind, he used a barely credible 190 metres, rotating hard at 50kt (93km/h), and then flew a 50kt (93km/h) approach to a positive 45kt (84km/h) touchdown, followed by heavy braking to stop in the same distance. This is amazing performance at a weight barely 100kg below maximum. Furthermore, I have read that Britten-Norman’s pilots used to demonstrate a takeoff on one engine alone, even then only using a ground roll of little more than 700 metres.

With STOL performance like that, it is no wonder the Islander has been so successful over the years, becoming nearly as familiar as the DC-3 in the same less accessible areas of the World. Cheaper than most other twins, it is simple, conventional, easy and inexpensive to operate and maintain and has an enviable reliability record. Its airframe may not be over sophisticated, but it is proven, and well suited to its many tasks, which include (but are not confined to) parachuting, coastal, offshore and inland surveillance, crop spraying, commuter and third level passenger work, air ambulance evacuation, geophysical survey, fire fighting, photography, pollution control, environmental and fishery protection, search and rescue, police pursuit and traffic patrol.

There are currently 22 Islanders on the Australian register, with six more 200hp (150kW) model BN2B-20s due to be delivered in the next year to National Jet for the Coastwatch coastal surveillance contract. Other recent sales have been in the Far East, including to Japan and China, in Africa and South America, and to the British police forces. It would seem that the enduring Islander can look forward to many more successful years ahead.