From Wikipedia (English):

Andrew Carnegie Whitfield (born 1910), the nephew of wealthy steel magnate Andrew Carnegie, mysteriously disappeared shortly after he departed from Roosevelt Field on Long Island, New York on the morning of April 17, 1938.

Early life

Whitfield was a graduate of Princeton University and had been employed as a business executive. An amateur pilot, Whitfield owned a small red and silver Taylor Cub airplane which he occasionally flew (mostly for recreation). At the time of his disappearance, he had accumulated 200 hours of flying experience.

Disappearance

When Whitfield departed in his small silver and red Taylor Cub monoplane, he had planned to land at an airfield in Brentwood, New York (approximately 22 miles (35 km) away). He was only supposed to be in the air for fifteen minutes, but Andrew never arrived as scheduled. One source reported that Whitfield's plane had been flying steadily—but then Whitfield "nosed his plane into a mild easterly wind, [and] disappeared from sight."

His plane had enough fuel for a 150-mile flight. Neither Whitfield nor his plane has ever been recovered.

An investigation discovered that (on the same day he vanished) he had checked into a hotel in Garden City on Long Island under an alias he occasionally employed: "Albert C. White." Hotel records indicated that Whitfield/White had paid $4 in advance for the room and never checked out. When the hotel room was searched, it was discovered that his personal belongings (including his passport), clothing, cuff links engraved with his initials, two life insurance policies (in his name listing his wife, Elizabeth Halsey Whitfield, as the beneficiary), and several stock and bond certificates made out in Andrew's and Elizabeth's names, were all left behind in the hotel room. Phone records also indicated that he had called his home while his family was out looking for him, and a telephone operator reported that she heard him say over the phone, "Well, I am going to carry out my plan."

Police concluded that Whitfield had committed suicide by deliberately flying his plane into the Atlantic Ocean despite there being no evidence to substantiate this theory. Although a thorough search of the coastal areas surrounding Long Island was conducted, no plane wreckage was ever discovered. There was no evidence that at the time of Whitfield's disappearance he was having any personal or business problems. Whitfield had married (the former Elizabeth Halsey) earlier that year and had been planning to move to Bethlehem, Pennsylvania (with his new wife) the same month that he disappeared.

From CharleyProject.org:

Vital Statistics at Time of Disappearance

• Missing Since: April 17, 1938 from Long Island, New York
• Classification: Missing
• Age: 28 years old
• Height and Weight: 5'8, 155 pounds
• Distinguishing Characteristics: Caucasian male. Graying brown hair, blue eyes. Andrew's nickname is A. C. He has an appendectomy scar on his abdomen, and one false upper front tooth.
• Clothing/Jewelry Description: A dark gray Brooks Brothers suit, a white shirt with an attached collar, low black shoes, a gray fedora, a silver wristwatch and a gold signet ring with an engraved dove on his left hand.

Details of Disappearance

Andrew departed in his small silver and red Taylor Cub monoplane from Roosevelt Field on Long Island, New York sometime after 9:00 a.m. on April 17, 1938. He planned to land at an airfield in Brentwood, approximately 22 miles away. He was only supposed to be in the air for fifteen minutes, but Andrew never arrived as scheduled. His plane has never been recovered. He had 200 hours of flying experience at the time of his disappearance, 50 hours short of the time necessary to obtain a commercial pilot's license, and was described as an accomplished pilot. His plane had enough fuel for a 150-mile flight.

Andrew checked into a hotel in Garden City on Long Island under the alias Albert C. White on the day he vanished. He paid $4 in advance for the room and never checked out. His personal belongings, including his passport; clothing; cuff links engraved with his initials; two $6,000 life insurance policies in his name listing his wife, Elizabeth Halsey Whitfield, as the beneficiary; and several stocks and bonds made out in Andrew's and Elizabeth's names; were left behind in the hotel room. Phone records also indicated that he called his home while his family was out looking for him, and a telephone operator says she heard him say over the phone, "Well, I am going to carry out my plan."

After this information was uncovered, police theorized that Andrew had committed suicide by deliberately flying his plane into the Atlantic Ocean. There is no evidence to support this theory; a thorough search of the ocean surrounding Long Island turned up no signs of plane wreckage and Andrew was not having personal or business problems at the time that he vanished. He had married in 1937, and had planned to move to Bethlehem, Pennsylvania the same month that he disappeared. Elizabeth sued Andrew for desertion after his disappearance. She explained that she did not believe he had deliberately abandoned her, but she thought the suit would be a way to better publicize his disappearance. Many people across the United States claimed that they saw Andrew for years after his plane vanished.

Andrew was the nephew of the steel tycoon Andrew Carnegie on Carnegie's wife's side. He was a graduate of Princeton University and was employed as a business executive in 1938. He was declared legally dead in 1946 and his case has long been closed by law enforcement due to the passage of time, but Andrew's disappearance continues to mystify people.