What Boeing supplied, and what the airline chose

The most surprising thing about the inside of a 747-400 is how little of it Boeing built. Air conditioning, pressurisation, water and waste, the oxygen the passengers breathed, the doors and the structure itself were all type-certificated content. The entertainment, the connectivity, the seat power and most of the seating were not. They were chosen, bought and fitted by individual airlines, usually several times over the life of the aircraft.

The proof is in the paperwork. The supplemental type certificate records for the 747-400 run to dozens of cabin-related approvals, and they are a far better guide to what a 747 cabin actually contained than any brochure.

What Boeing did supply

The airframe and its services, described in the airport-planning documentation:

• Two-crew cockpit with digital avionics - the -400 was where the engineer finally went away, and the flight deck was rebuilt around EICAS.
• An upper-deck cabin on the stretched fuselage, and an optional crew rest compartment in the aft cabin - a long-haul feature rather than a luxury one, on an aircraft whose sector times were routinely ten hours and more.
• Vacuum lavatories with single-point servicing, covered on their own page, and a cabin designed around the single aisle of the original type.
• Electrical power and pathways for cabin equipment, drawn from the same distribution described in the electrical system page, plus the recirculation and air distribution that the pressurisation page covers.
• Ground servicing connections - conditioned air, electrical power and water - which the airport planning documentation treats as a fixed interface. On a freighter or Combi that also means loading equipment, covered under the cargo-loading system.

That is the boundary. Boeing delivered an aircraft with a functioning, certified cabin. Everything the passenger actually touched beyond the seat cushion and the window shade was somebody else's decision.

Entertainment and seat power

Entertainment and seat power were, in practice, a single package. Approved 747-400 modifications repeatedly pair them: a Panasonic System 3000i in-flight entertainment system installed together with an Astronics in-seat power supply, for instance, on a 747-400 operated by a cargo conversion specialist. The same pattern shows up across the approved modification record, because a seatback screen and a socket at the same seat are the same installation decision.

The consequences of that arrangement are worth spelling out, because they explain the economics of the type:

• Airlines could differentiate. Two airlines operating identical 747-400s could have materially different cabins, which was a genuine competitive lever on long-haul routes.
• Upgrades were cheap to defer. Entertainment technology moved fast; deferring a refit for a few years cost passengers very little and saved the operator a great deal.
• The aircraft changed repeatedly. A single airframe could carry three or four different entertainment systems, four different seat sets and two different connectivity solutions across thirty years of service. Every one of those transitions is a line in the type certificate record.

The cost is complexity, and it shows up in the weight and balance manual rather than in the cabin. Cabin equipment, seating and crew provisions are all part of the operator's weight and balance data, and a change of seat specification or a different entertainment installation moves the aeroplane's empty weight and its centre of gravity. See also the site's seating layouts and interiors sections.

Connectivity came late, and by certificate

Satellite service on the 747-400 arrived entirely through approved modification, and the records show a clear progression:

Stage	What it provided
High-gain SATCOM voice	The cabin public telephone, fitted on 747-400s by individual operators
AIRSAT II provisions	Wiring and antenna provisions installed in advance of a later installation
Rockwell Collins AERO H+ SATCOM	A dedicated satellite system for the cabin
Iridium and Iridium-based systems	Lightweight satellite voice and messaging
Connexion by Boeing	Satellite television, and then the data service that became in-flight internet
Cabin wireless LAN	Passenger and crew devices connecting to aircraft systems

The high-gain cabin telephone is a good illustration of how narrow the line between the flight deck and the cabin can be. An approval held by a major US airline for the 747-400 reads simply: "Installation of High-Gain Satellite Communication (SATCOM) voice system for cabin public telephone." The same antenna architecture that serves the flight deck's data requirements was extended to the cabin, and the public could telephone home from seat 34K.

The heat problem

One consequence of all this is thermal. Seatback electronics, seat power supplies, video distribution and cabin network racks all produce heat, and a pressurised cabin on a type whose basic layout was settled in the 1960s has a fixed cooling capacity. The system therefore has to reject a considerable amount of waste heat without compromising the passengers, and a cabin equipment change is not purely a commercial decision - it interacts with the air distribution, the pressurisation and the electrical system at the same time.

A deliberately mixed cabin

The minimum equipment list treats most of this as dispensable. Passenger convenience items may be inoperative or missing, and the lavatory ashtray entry that appears in the approved 747-400 supplement is a small illustration of the philosophy: a cabin feature can be allowed to fail without grounding the aeroplane, provided the associated safety systems remain operative.

The safety-critical cabin equipment is of course not treated that way. The cabin is where the oxygen, the fire detection and the evacuation systems live, and those are certified content on every 747 built.

Related

• Pressurisation - the air the cabin actually breathes
• Oxygen system - crew and passenger masks
• Doors and emergency exits - the evacuation system
• Weight and balance and loading - where every cabin change is recorded