On early examples and even some of the later On Mark conversions,
some aircraft did not incorporate the circumferential “ Ring “ rear spar, and had the belly Airstair as the
The cabin was broken up into compartments that limited
comfort and ease of movement.
On Mark was able to open up the interior considerably
with the incorporation of the rear “ Ring “ spar that eliminated the original aircraft’s carry-through structure
/ partial bulkhead. This option first appeared on the prototype Marketeer, N40Y in 1957. The ring spar eliminated the difficulty
in having to duck under the rear spar carry-through structure, and to navigate around the area in the cabin floor for the
bottom entry door. Ring spar optioned versions of the Marketeer, and all Marksman conversions had the starboard side Airstair
entry door, and the mid-cabin seats could now be mounted on tracks to allow arrangement flexibility and ease movement about
the cabin. On Mark named their interior arrangement options
as " The Director ", " The Administrator " and " The Secretarial "
The Invader’s fuselage width was so narrow that
passing between two adjacent seats was very difficult, so was usually avoided. To compensate, On Mark designed the cabin to
have a long couch installed along the port side with it’s back bisected by the ring structure, or individual chairs
installed fore and aft of the rear spar. The couch or these individual chairs faced to starboard. Two opposite footwell windows
below the wing gave the passengers seated there a view out from that mid-section seating area. The fully enclosed lavatory
( when optioned ) was port-side forward just behind the aft face of the forward spar bulkhead, and was just big enough to
have a very small wash basin on the forward wall and a chemical toilet installed in the aft-portside area. There was just
enough floor space to stand ( on the Marketeer and early Marksman conversions, stoop ) at the wash basin just inside the angled
privacy door, and the closed toilet lid made for a jump-seat.
The aft most seat pair ( double seat ) was just far enough
forward of the rear cabin bulkhead to allow reclining to around 20 degrees from vertical. As the fuselage was beginning to
further narrow in this area, these seats were very close together and shared a center armrest. Retractable footrests could
be extended forward from beneath the rear double seats on most conversions for comfort. Work tables were held in wood paneled
pockets along the outboard sidewalls, lifting up and folded out horizontally to bridge across the cabin for use by the rear
and aft-intermediate cabin seat occupants. These intermediate area seats ( mounted on tracks for fore-aft adjustment ) could
be positioned facing either forward or aft, individually or in pairs. Large cabin windows were installed in the fuselage sides
for these passengers. Small “ brow “ type windows were installed in the fuselage above the wing to brighten this
area of the cabin. Curtains were usually installed and could be drawn closed to cover all cabin window openings.
Beverage and food service consoles could be optioned and
were usually installed on the cabin’s starboard side, inboard of the wing root area. Entertainment equipment, and flight
status instruments could also be included, tucked into small consoles between seats or on dedicated panels. Emergency escape
hatches were provided in the cabin overhead.
Whatever interior arrangement was chosen, entry to the
cockpit-flight-deck was accomplished by ducking under the forward spar through an opening on the starboard side. The cockpit
floor was the ceiling of the nose gear well and therefore elevated from the cabin floor. An angled bulkhead extended from
the top of the aft nose gear well bulkhead, rising up to the base of the forward wing spar carry-through. This panel was solid
for 2/3rds of the width towards the port side, open on the starboard 1/3rd for cockpit entry. The cockpit jump seat ( when
optioned ) was mounted on the port side behind the pilot.
All interior appointments were of the highest quality
and comfort levels. On Mark worked with each of their customers to provide an environment that was as unique, plush, and as
quiet as possible. These interiors far exceeding the standards of the best the airlines had to offer, and set an example for
other business aircraft to follow.