THE Provisional IRA may be preparing a major atrocity within the next

few weeks following the success of an ambush on Sunday when it lured

Scots troops to within yards of the Eire border and machine-gunned an

unarmed helicopter, forcing it to crash-land in County Tyrone.

Intelligence sources in Ulster are still refusing to say whether the

helicopter, a Gazelle light reconnaissance model, was hit by any of the

300 rounds the IRA claims to have fired at it. None of the three men

aboard was wounded by gunfire, although one has serious back injuries

caused by impact damage.

It is believed that the East Tyrone PIRA, one of the toughest in

Northern Ireland, staged a diversionary ''come-on'' operation by driving

a number of vehicles in a sensitive border area to draw Army attention.

The Army responded with a foot patrol of the King's Own Scottish

Borderers backed up by a Gazelle helicopter flying top-cover for the men

on the ground. It is not yet clear whether the terrorists planned

initially to shoot down the helicopter or ambush the infantry.

But they used at least two heavy-calibre machine-guns -- either

American M60s or Soviet-made and Libyan-supplied 12.7mm weapons -- and a

number of automatic rifles to carry out the attack. The helicopter

plunged into a field near the border. Two Army Air Corps pilots were

slightly hurt, and a sergeant-major from the KOSB suffered spinal

injuries in the crash.

The damaged aircraft, which normally carries one or two of a crew and

a maximum of two passengers, is now under armed guard while it is

examined by forensic and aviation experts.

Helicopters are prestige propaganda targets. Only one previous

aircraft, a Lynx, was brought down by gunfire in 1988 in South Armagh.

It was the first casualty of its kind in the 20 years of conflict in the


In December last year, the South Monaghan PIRA, aided by local

activists, mounted a mass attack involving more than a dozen gunmen on a

KOSB vehicle checkpoint at Derryard in County Fermanagh only a few yards

from the border. Two soldiers died and a third is still in hospital.

The terrorists are believed to have intended to wipe out the nine-man

garrison of the outpost as a pre-Christmas coup. The assault was carried

out using rocket launchers, machine-guns, automatic rifles, grenades and

a flame-thrower. It was foiled by the intervention of a four-man Army

patrol which appeared unexpectedly and drove off the attackers with more

than 100 rounds of small arms fire.

The authorities now believe that a further strike against the KOSB has

been planned to mar the end of the unit's tour in Ulster. The battalion

has found considerable quantities of Semtex, the IRA's favourite

explosive, and uncovered a number of weapons' hides in the

Tyrone-Fermanagh area during its four months' stay in the province.