52 Doors and Introduction to Zone & Station identification

TTP		ATA 52
Beech 90 Series	B1-L3	Doors
	B2-L1
	B2-L1	Introduction to Zone & Station identification
	B2-L1

CABIN ENTRY DOOR

The cabin entry airstair door is on the left side of the fuselage, just aft of the wing. A swing-down door, hinged at the bottom, provides cabin pressurization and security for flight and a convenient stairway for entry and exit. Two of the three steps are movable and automatically fold flat against the door in the closed position. Two plastic-encased  cables, one at the forward edge and one at the aft edge of the door, provide support for the door in the open position, a hand- hold for passengers, and a means of closing the door from inside the aircraft. Originally only the aft cable was installed. Later the forward cable was optional, but current production aircraft have both cables installed.

The aft cable can be temporally unhooked and positioned out of the way to load or unload bulky items. A hydraulic damper permits the door to lower gradually during opening. It is important that not more than one person be on the airstair door at a time, as excessive weights could cause structural damage to the door.

A red CABIN DOOR annunciator, on the glareshield annunciator panel, illuminates to indicate the cabin entry door is open or not securely locked. An inflatable rubber door seal around the cabin door expands to seal the pressure vessel while the aircraft is in flight. Air from the aircraft pneumatic system, reduced to 4 psi, provides the source of pressure to inflate the seal.

 Two  mechanically  interconnected  handles,  one on the outside and one on the inside of the door, operate the door latching mechanism. For ground security, a key lock is built into the external handle. When the handle is rotated to the closed or locked position, two latch bolts at the front edge and two latch bolts at the aft edge of the door, and two latch hooks at the top of the door, lock  into  the  doorframe  to  secure  the  airstair door. Over each locking bolt there is a sight opening on the inner facing of the door. When the door is locked, a green stripe on the lock bolt aligns with a black pointer in the sight opening.

Whether unlocking the door from the outside or the inside, the release button adjacent to the door handle must be depressed before the handle can be rotated (counterclockwise from inside the air- plane, clockwise from outside) to unlock the door. Consequently, unlocking the door is a two-hand operation requiring deliberate action. The release button acts as a safety device to help prevent accidental opening of the door. As an additional safety measure, a differential-pressure-sensitive diaphragm is incorporated into the release-button mechanism. This is true when either the outside or inside release button is depressed. Addition- ally a small round window, just below the first step, permits  observation  of the  pressurization safety lock mechanism. A placard adjacent to the window depicts the proper position of the safety lock arm around the bellows shaft. A red button light switch adjacent to the window controls a lamp inside the door to illuminate the safety lock mechanism.

EMERGENCY EXIT 

An emergency exit door is at the third cabin window, on the right side of the fuselage. A placard on the emergency exit hatch release cover lists the proper opening procedures. The door is released from the inside with two hooks, a trigger button, and a latch-release pull- up handle. A pressure diaphragm lock, similar to the one on the cabin entry door, prevents the door from being opened when the cabin is pressurized. If pressurized, pulling the hooks override the pressure lock and allows the trigger button to be depressed. This releases the latch-release handle. When the handle is pulled up and the securing latches are released, a hinge at the bottom allows the hatch to swing outward and downward for emergency exit. An inflatable rubber door seal around the cabin door expands to seal the pres- sure vessel while the aircraft is in flight. Air to inflate the seal comes from a tee in the line that inflates the cabin entry door. The emergency exit door can only be opened from the inside of the aircraft.

 

CABIN DOOR WARNING SYSTEM 

The red CABIN DOOR light in the annunciator panel remains illuminated  until the cabin door is closed and the handle is locked. The circuitry is controlled through two microswitches, one in the doorframe and one contained within the door. When the door is closed and locked, the lower forward latch bolt moves a spring tab, actuating a switch behind the striker plate in the doorframe. When the handle is rotated to the locked position, the latch arm actuates the switch inside the door adjacent to the lock assembly. With both of these switches closed a ground is provided to the annunciator circuit to turn the CABIN DOOR light off.

NOSE BAGGAGE DOOR

 

The King Air C90A/B/GT through LJ1530 has a 16-cubic-foot nose baggage compartment, which is accessible through a door on the left side of the nose. The baggage door is hinged at the top to allow the door to swing upward. A flush-mounted door handle with a push-to-release button operates three bayonet-type latching bolts. When the handle is rotated to the closed position the  latching  bolts  extends  into  the  doorframe structure  and  hold  the  door  securely  closed. When the handle is rotated to the open position, a switch in the doorframe structure for the forward latch bolt, opens and the red BAG DOOR OPEN light in the annunciator panel illuminates. In addition, the door is equipped with a secondary safety latch to hold the door in a partially closed position if the latching bolts are not engaged. For security the nose baggage compartment door features a key-lock latch. Starting with LJ1531 aircraft are equipped with a standard access panel and are no longer fitted with the baggage compartment door.

PTP  Beech 90 Series	B1	LOC	FOT	SGH
	B2	LOC		SGH