Flight Impressions – BAe 125-F400

The cost of this transformation was a few knots in cruising speed and some airfield and climb performance but range and fuel efficiency was what the customers wanted. The -700 went on to become the biggest selling version of the 125 thus far with 215 delivered over its seven year production run, although the current Series 800 with more powerful Garretts, a redesigned wing, longer range and other refinements is very close to that figure. Total 125 sales are approaching 800. 125 Retrofits

The success of the 125-700 served to inspire the instigation of a retrofit program for older 125s involving the installation of TFE731-3 powerplants. The vast majority of 125s had (and still have) used only a fraction of their airframe lives and a useful market for such a conversion was perceived to exist. Two such programs were established, one in the United States by AiResearch Aviation and the other in Britain by Hawker Siddeley/BAe.

The conversion could be applied to short fuselage Series 1NB, 3NB, 3NRA, 38/RA and 400 aircraft along with the longer fuselage Series 600. The first -700 had in fact been a -600 converted. The only models to miss out were the original Series 1s (only eight of which were built) and the Series 2 Dominie navigation trainers operated by the Royal Air Force.

When converted to Garrett engines, the aircraft were redesignated by adding an ‘F’ prefix to the series number. The 125-400 became the 125-F400, for example, while aircraft converted by AiResearch were marketed under the generic title ‘731 Hawker’.

The result was an efficient and quiet corporate jet which retained the main virtues of the 125 up to that point – its spacious cabin and excellent flying qualities – and could be had in the late 1970s for just over $US3m, a price slightly more than half that of a new and furnished -700. Apart from the benefits of extra range, the shorter fuselage 125s also gained improved airfield and climb performance due to the increased thrust provided by the TFE731s in combination with operating weights which remained as before. The fuel efficiency of the conversion is well illustrated by the fact that in the cruise a fuel flow as low as 1,200lb/hr is possible – a figure similar to that achieved by a Viper powered 125 while taxying on the ground!

The conversion programs are now essentially complete with some 80 aircraft converted including 12 -600s, 52 -400s/3ARs and 16-1N3N3Bs.

The matter of converting the 125s to take the new engines was not simply a matter of bolting them on to the sides of the aeroplane. Hundreds of detail changes were required but the main ones included the installation of a more powerful double rudder bias strut (to cope with the asymmetric situation as the larger diameter Garretts are further apart than the Vipers), installation of a new engine beam, reskinning of a large proportion of the rear fuselage, reworking of the rear fuselage to reinforce the area adjacent to the turbines in case of turbine disintegration, fitting a ventral fin of increased area, replacing the engine pods, modifying the fuel system adjacent to the engines, modifying the hydraulic system and installing variable delivery pumps and revising the electrical system to make it compatible with the Lear-Siegler starter generators fitted to the Garretts.

Inside, a new central instrument panel is installed containing new instruments appropriate to the Garretts and including two RPM indicators for the two shaft engines. The annunciator panel was also altered. Most aircraft also had their interiors upgraded to the latest standards when converted and the extra range capability of the aircraft dictated the installation of a long range Omega/VLF navigation system. Some were even fitted with EFIS instrument panels.

Sampling the ‘731 Hawker’

Thanks to the good offices of Mr Rex Banks, Pacific Aviation’s Manager of Charter and Flight Operations, I was able to briefly sample the delights of travelling in a 125-F400 on a quick trip from Sydney to Canberra and return. VH-PAB is the first Garrett 125 conversion to arrive in Australia and is available from Pacific for charter or sale. In command on the flight was the company’s Chief Pilot, Captain Barry Costain.

VH-PAB began life in November 1971 when (as a Series 400A) it was delivered to Beechcraft-Hawker Corporation in the USA (at that stage Hawker Siddeley had a marketing agreement with Beech covering the 125) from where it went to its first owner, Yellow Page Aircraft Inc, the following month. PAB was the 265th HS. 125 built, and its previous identities include N63BH, N711Y P and N125MD.

It is said that first impressions mean a lot, and in the case of PAB it was one of having to remember that here was an aeroplane nearly 20 years old. Inside and out it was pristine and could have come off the production line last week. The interior has been upgraded and features seven passenger seats, three individual chairs on the port side of the cabin (the front pair in ‘club’ arrangement), a three seater divan on the starboard side front and another individual seat at the rear. Behind that is an airline sty!e toilet_, while a galley is immediately aft of the entrance airstair door In the port forward fuselage and a TV/video screen is mounted on the bulkhead immediately forward of the divan and aft of the baggage compartment.

The 125’s biggest selling point has always been its cabin which is high enough for a large proportion of the population to stand up straight in and requiring only a slight stoop for the rest of us. Anyone taller than dwarf size (and who has had to crawl on hands and knees to his seat in a 20 or 30 series Lear) will appreciate this, especially those of us who are well above average in my case 6ft 4in (1. 93m). ‘

For our flight to Canberra we were carrying the required two aircrew, f?ur passengers in the back and 4,700Ib of fuel, giving a ramp weight of 19,300lb, well below the maximum permitted of 23,800Ib. At this weight, rotation speed (Vr) was calculated at 111 knots indicated airspeed (KIAS), V2 was 113KIAS and initial climb speed was 151KIAS.

After a few minutes’ delay at the holding point waiting for an RAAF Boeing 707 to depart, Barry Costain began PAB’s takeoff roll at 1112hrs local time. Fifteen seconds later and after real ‘kick in the back’ acceleration the 125 was airborne and on its way to Canberra. At ourweight the aircraft was capable of climbing at better than 4,500ft/min.

It’s only 126 nautical miles (233km) from Sydney to Canberra, so most of the leg was spent either climbing or descending with only a very brief cruise phase. Peak altitude reached was 26,000ft (area Wollongong), outside air temperature was -41 deg c, true airspeed 365 knots and fuel flow 1,400Ib/hr. At higher altitudes that could be reduced to 1,200lb/hr. Apart from the fuel flow, this information was displayed for the passengers’ benefit in digital form on the forward bulkhead, the readout keeping track of speed (in miles per hour as this was an aircraft purchased from the USA), altitude and outside air temperature.

Back in the cabin, the passengers were sampling the pleasures of corporate jet travel – comfort, a hot snack from the galley and a cold orange juice.

We performed a touch and go at Canberra and then it was straight up to 27,000 feet for the journey back to Sydney. The outward journey had taken 32 minutes from lift off to touchdown. The return journey taking just 28 minutes from liftoff to touchdown in Sydney, giving a total trip time of exactly one hour. For once, the extra hour’s holding fuel now required for operations into Sydney wasn’t required, the 125 being permitted to go straight in – “for the first time in recent memory”, according to Barry Costain. The initial approach was flown at 118KIAS, reducing to 108KIAS ‘over the hedge’ . The braking action was smooth and powerful, resulting in a short roll.

An analysis of the flight revealed a total fuel consumption of 1,700lb, an economical performance considering the nature of the flight with its short stages and two takeoffs and climbs. At the other end of the scale is the fact that the F400’s range enables it to fly Australia’s most difficult longer stages non stop. Sydney to Perth (1,776nm), for example, can be comfortably flown against the most probable and substantial headwinds and with the stringent Australian fuel reserves still on board at the end of the flight. Similarly, Melbourne to Darwin (1,723nm) and Darwin to Singapore (1,810nm) are in comfortable reach.

The package is an impressive one which for the money is very difficult to beat in an aircraft which is appreciated by both passengers and crew. In fact, there may even be a case for putting a Garrett engined ‘short fuselage’ 125 back into production for those who find the airframe/powerplant/range combination adequate for their needs.

Pacific Aviation offers VH-PAB for charter at around $3,000 per hour or for sale at $US3. 85m comprehensively equipped including a GNS-500A long range navigation system, flight data recorder and cockpit voice recorder. The company also offers partial or full management of the aircraft to any purchaser including technical, financial, crewing, maintenance and charter to other clients.

Our thanks to Rex Banks and Pacific Aviation for the chance to sample this delightful aeroplane.