The rarest passenger airliner you’ve (probably) never heard of: the Lockheed L-100-30(P).
In the early 1990s, Indonesian carrier Merpati Nusantara turned two civilian Hercules freighters into full passenger airliners. Only two aircraft ever received the conversion — PK-MLT (shown here) and PK-MLS.
Lockheed’s Aeromod Center in Greenville, South Carolina cut 22 Boeing 727 windows into the fuselage, added emergency exits, galleys, lavatories, and structural reinforcements. Inside: a fully carpeted cabin with 97 coach seats in a mix of 3-3 and 3-2 abreast. Baggage rode on the rear ramp.
These unique “airliner Herks” served remote Indonesian routes for about five years before Merpati replaced them with Fokker 100s. No other airline ever ordered the passenger conversion.