were already into flight certification. To expedite development, Boeing used 60% of the structure and systems of the existing 727, particularly the fuselage, which differs in length only. This 148-inch (3.76 m) wide fuselage cross-section permitted six-abreast seating compared to the rivals' five-abreast. The 727's fuselage was derived from the 707.

The proposed wing airfoil sections were based on those of the 707 and 727, but somewhat thicker; altering these sections near the nacelles achieved a substantial