Charles A. Appel, 86, who operated his own business as an examiner of questioned documents after retiring as an FBI agent in 1949, died Friday at Sibley Memorial Hospital after a heart attack. He lived in Washington.

First as an FBI agent and then in a private capacity, Mr. Appel was a technical witness in cases involving some of the era's most famous and controversial people and events.

A questioned documents expert examines not only handwriting, but the paper itself and how it was made, the composition and age of the inks and dyes used in documents, and ways documents in question may have been altered.

He was a witness in trials involving senator Thomas Dodd (D-Conn.), Aristotle Onassis and Howard Hughes. He also testified in the Lindbergh kidnaping case.

Mr. Appel was born in Washington. He was a graduate of McKinley High School and the law school of George Washington University. He served in the Army in World War I. He began his 25-year FBI career two years later. He was assigned to several field offices and then to Washington.

In 1931, Northwestern University offered a course on the scientific examination of documents. With the approval of J. Edgar Hoover, Mr. Appel took that course, graduating at the top of his class. He returned to Washington as chief of the documents section of the FBI Laboratory and held that post until he retired in 1949.

Since then, he has been an independent questioned documents expert.

Mr. Appel was a member of the Society of Former FBI Agents and of the Blessed Sacrament Catholic Church in Washington.

Survivors include his wife, Mary C., of Washington; five sons, Charles A. III, of Los Angeles, William M., of Chicago, Edward J., of San Francisco, Peter B., of Charlottesville, and Paul C., of Miami; two brothers, William D., of Albuquque, N.M., and Frederick W., of Washington; two daughters, Maryann Rankin of Front Royal, and Margaret Munn of Tampa, Fla.; 16 grandchildren, and four great-grandchildren.