AIRCRAFT frame-makers Boeing and Airbus Industrie and a host of engine manufacturers have been rolling out the red carpet for Singapore Airlines (SIA) since it announced its plan to order up to 52 additional aircraft in the next few months. The orders, worth about S$10 billion (about HK$49.03 billion), are in addition to the 26 aircraft SIA already has on firm order and its options on a further 28. US-based Boeing has been invited to bid for additional firm orders for 11 long-haul Boeing 747-400 aircraft, commonly known as Megatops, and for options on 11. SIA already has 23 Megatops and 14 slightly smaller Boeing 747-300 Bigtops in its passenger fleet, while the cargo fleet consists of four Boeing 747s and one Boeing 737. Airbus of Europe has been asked to bid for a contract to supply 15 long-haul A-340s on firm order and a further 15 on option. It already has options for 13 long-range A-340s. Four engine makers are bidding for the Boeing 747-400s and A-340s. They are General Electric, CFM International, Rolls-Royce, and Pratt & Whitney. Pratt & Whitney could well be a winner given that it has signed two joint-venture agreements for jet-engine repair services in the Asia-Pacific region with SIA Engineering and has previously supplied power plants for SIA's Boeing 747 fleet. All the frame and engine makers are believed to have submitted their bids and SIA said it would decide on its order within the next two to three months. The proposed order, which matches in size the recent US$6 billion aircraft order of Saudi Arabian carrier Saudia, is aimed both at keeping the average age of SIA's fleet young and to allow for expansion. SIA expects to grow at about eight per cent a year, and says it will need to add 40 to 50 aircraft to the fleet by the turn of the century. The new planes are likely to be wanted for delivery between 1997 and 2003. Although SIA has been quite specific about the numbers and types of aircraft it is looking to buy in its briefings to both manufacturers, it said it was remaining flexible about its future aircraft requirements. ''SIA will not rule out introducing another size of aircraft, something between the A-310 and A-340,'' a spokesman said. This could suggest SIA may be also looking for a smaller regional aircraft, capable of carrying between 180 and 270 passengers on short-haul routes in Asia. SIA has not yet sought bids for this type of plane, leaving the field wide open for another scrap among airframe manufacturers. If history is to be repeated, SIA is likely to opt once again for the 186-seater A-310. It already has 19 of the aircraft in its fleet to distribute traffic to and from its far-flung markets. McDonnell Douglas and Boeing were both victors in the Saudia battle, although McDonnell Douglas can be expected to sit on the sidelines this time round. SIA does not have any McDonnell Douglas aircraft in its 61-strong fleet and is unlikely to start now for compatibility reasons. SIA has not given any idea how the airline intends to finance the proposed purchases. Previously, it has managed to keep its ambitious fleet renewal programme rolling by selling ageing aircraft as soon as new replacements arrived. The average age of its fleet stands at just five years. However, with the worldwide aviation slump and a glut of second-hand aircraft, SIA has been experiencing a few hiccoughs with its cash flow. Last year, it managed to dispose of only two aircraft - and that was to its subsidiary Silk Air, and this was said to have been at very favourable terms.