Air Crashes Cast Doubt on Combat Readiness : Military: Officials are worried as pilots encounter unanticipated problems navigating the desert at night.

A series of after-dark crashes of U.S. military aircraft has exposed unanticipated problems in desert navigation, prompting some commanders to question whether pilots are fully prepared for possible night combat, according to military officials.

The ability of U.S. pilots to wage war unrestrained by darkness was considered to be one of the United States’ signal advantages over Iraqi forces. Most U.S. contingency plans rely heavily on the assumption of a superior ability to launch attacks after dark. But the crashes have called into question the common boast that “we own the night.”

An Army official acknowledged Wednesday that its top commanders here had ordered significant limits on helicopter night training after two choppers plunged into sand dunes about a month ago. Two more Army helicopters have crashed at night since the restrictions were imposed.

Altogether, 10 U.S. servicemen have been killed and nine injured in nighttime crashes of seven helicopters and an airplane in and near Saudi Arabia. Although all the crashes remain under investigation, aviators point to blowing sand, the difficulty of flying with night-vision goggles, and terrain so featureless that it is difficult to differentiate sky and land.

“It’s not easy finding the ground sometimes,” one Army pilot said of the desert conditions.

“We don’t view it as bringing into question our ability to fly and fight at night, but it does show the difficulties our pilots experience flying in that environment with night-vision devices,” a senior Marine commander in Washington said.

“All pilots have bad days. And when you have a bad day on night-vision devices, it could be your last,” he added.

The Air Force, Navy and Marine Corps have not yet restricted night flying missions here, officials here and in Washington said Wednesday.

But with their helicopters and fixed-wing planes plagued by similar problems, the officials said there is no doubt that pilots have had considerable difficulty in coping at night with the deceiving desert terrain.

“There’s a lot of new things to hit in the desert,” one official said. “And when it’s dark out, we seem to be doing a pretty good job of running into them.”

In the most recent incident, an Air Force F-111 fighter-bomber crashed in the southern Arabian Peninsula before dawn Wednesday, killing both crew members in the fourth fatal U.S. military crash in three days.

The pilots were identified as Capt. Frederick A. Reid of Harrisburg, Pa., and Capt. Thomas R. Caldwell of Columbus, Ohio.

Also Wednesday, the Navy announced that it had called off its search for the eight Camp Pendleton-based Marines presumed killed in the worst night-flying accident here to date. The two helicopters apparently collided early Monday and crashed into the Arabian Sea.

The accident Wednesday brings to 31 the number of U.S. servicemen killed so far in Operation Desert Shield--a number that top military officials insist is not excessive given the number of soldiers and operations involved in the massive U.S. deployment.

But privately, the officials acknowledge that the high rate of accidents in the region involving aircraft flying after dark has become a particular source of concern rmong commanders.

“What we have and (the Iraqis) don’t is a 24-hour capability. They don’t use their air force at night. It makes a difference when you can apply air power 24 hours a day,” Lt. Gen. Thomas R. Ferguson Jr., commander of the Air Force’s aeronautical systems division, said in a recent interview.

But, he acknowledged, “we don’t have anything that can see through a desert sandstorm.”

Military officials in Saudi Arabia said that the propeller wash from a hovering or low-flying helicopter can create the equivalent of a sandstorm.

And they note that the desert, not easy to fly across even by day, becomes even more hazardous at night, when shifting sand dunes suddenly loom from nowhere and dark desert floor and dark sky can appear indistinguishable.

At the same time, aviators say, sand blown by the low-flying helicopters can incapacitate pilots by obscuring the stars and moonlight on which their night-vision goggles depend. Pilots also can become disoriented and lose the horizon because ground and sky are the same color--a phenomenon fliers call the “milk-bowl effect.”

A Marine aviator said that the featureless terrain of the Arabian Peninsula is one of the toughest flying environments in the world. “You really have to depend on your instruments,” he said. “But the more you fly, the better you get.”

Under the new guidelines for the Saudi desert ordered here by Army Lt. Gen. Gary Luck, who as commander of the 18th Army Corps oversees all Army aviation units here, helicopter pilots must maintain an altitude of at least 150 feet.

The regulation represents a major constraint on pilots who normally seek to emulate possible combat missions by hugging the terrain.

At the same time, officials said, additional Army guidelines for the Saudi desert now require that two pilots be present at the controls during night operations and that disoriented pilots maintain their altitude rather than risk a descent to look for the ground.

An Army spokesman, Maj. Dan Grigson, said that the altitude restriction, imposed about 30 days ago, will remain in effect indefinitely until U.S. pilots become fully accustomed to the desert terrain.

But Grigson said that the Army hopes to accelerate the orientation process through training. And while acknowledging that the current restrictions rule out combat-type operations at night, he said: “If it would go to combat, I think the 150-foot limit would be dropped almost immediately.”

The eight Camp Pendelton-based Marines were identified as: Capt. Gary S. Dillon, 29, of Merrimack County, N.H.; Capt. William D. Cronin Jr., 29, of DuPage County, Ill.; Capt. Kevin R. Dolvin, 29, of Stark County, Ohio; Capt. William J. Hurley, 27, of Cook County, Ill.; Sgt. Kenneth T. Keller, 26, of Cook County, Ill.; Sgt. John R. Kilkus, 26, of Norfolk County, Mass.; Cpl. Timothy W. Romei, 22, of San Francisco, and Lance Cpl. Thomas R. Adams, 20, of Baton Rouge County, La.

Jehl reported from Saudi Arabia and Broder from Washington.

F-111 Two-seat fighter-bomber Wingspan: 63 ft. (fully spread) Length: 73 ft. 6 in. Maximum speed: 1,650 mph. Range: 2,925 miles Built by: General Dynamics Entered service: 1967 Armament: SRAM missiles Nuclear bombs Sparrow, Sidewinder or AMRAAM air-to-air missiles Maverick TV-guided missiles GBU-12/ -24 laser-guided bombs GBU-15 TV-guided bombs Gravity bombs Sources: Jane’s All the World’s Aircraft, Modern Attack Aircraft