Airways: "Today, in 1972, Lockheed L-1011 TriStar (N301EA) entered commercial service with Eastern Air Lines on its Miami-New York route"; Lockheed Martin[2]: "After its revenue flight on April 26, 1972, Eastern Air Lines began the scheduled operation of the L-1011 on April 30". The delivery date varies between sources (Wikipedia[3] gives both 5 and 26 April), so the pin uses the revenue-flight day.
The Lockheed L-1011 TriStar, N301EA, entered commercial service with launch customer Eastern Air Lines on 26 April 1972 on the Miami to New York route, making it the third wide-body airliner in commercial operation after the 747 and DC-10.