ARLINGTON, Va. (AP) _ Martin Vanden Eykel II was told to beware the mountain.

The Army doesn't know whether the helicopter pilot from Illinois slammed his aircraft into rock or was killed by enemy fire during a night mission in Vietnam.

But on Friday, nearly 21 years his death, his remains and those of three fellow soldiers were buried at Arlington National Cemetery.

''The void will always be there because I lost my son,'' said Wilma Vanden Eykel. ''But I'm glad that instead of wandering the jungles for 20 years he is with the Lord.''

The remains of her son, of Wheaton, Ill., were buried with those of William D. Sanderlin of Fort Worth, Texas, Michael H. Shanley Jr. of La Mesa, Calif., and William C. Dunlap of Tucson, Ariz.

An Army band marched to the grave, leading the horse-drawn carriage that carried the casket. On an otherwise cool and cloudy day, the sun suddenly appeared as the band leader raised his baton for ''Amazing Grace'' and the mourners settled in velvet-covered chairs.

The chaplain, Lt. Col. John W. Morrison, said a short prayer and blessed the casket. A group of soldiers fired three loud volleys, and a bugler followed with ''Taps.''

''We still have a great pain in our hearts for all the boys who are still missing in Vietnam,'' said Maury Vanden Eykel, brother of the fallen pilot.

''We'd like to see some answers for their families, too,'' he said.

On Dec. 2, 1969, Vanden Eykel and the other soldiers were aiding American ground troops by firing flares during night combat. Another helicopter on the same mission warned that both aircraft had to change course to avoid a mountain.

Vanden Eykel, 26 at the time, said he felt dizzy. He acknowledged the warning, but his helicopter soon disappeared. It was never found despite a four-day search.

Vietnam returned 25 sets of American remains in January 1989. The identities of Dunlap, a chief warrant officer, and Sanderlin, a staff sergeant, were confirmed through dental records.

Vanden Eykel, a chief warrant officer, and Shanley, a sergeant, have never been positively identified. But two months ago, a military board ruled that the men's remains were included with those of Dunlap and Sanderlin.