The Handbook of Instruction for Designing and Constructing Airplanes (Home Flight Construction 7)

All occupants shall be provided with parachutes. Figure 3 shows the general construction of seats. As a rule, the pilot and other occupants who remain seated on a stationary seat will use a seat type pack, and all occupants who are required to move about, such as gunners and observers, shall use the lap type pack. The seats and cockpits must be so designed that the occupants may leave the cockpits suddenly without danger of the packs catching on an obstruction and so they may sit comfortably and be in proper relation to the controls, etc. There must be sufficient clearance between the upper wing and fuselage and between the bracing members to permit the occupants to leave the cockpits easily and clear the airplane, in case a parachute descent is necessary.