Community Thu, 21 Jun 2018 06:14:48 +0000 MYOB en-gb Mark created a new forum post in ATA 35 Oxygen
King Air's use a cabin altitude sensing switch for automatically deploying the passenger masks when cabin altitude exceeds approximately 12,000 feet. (I did not investigate it, but I believe another switch is used for crew warning.)

The switch is located in the forward cabin, right side-wall, just forward of the emergency exit.

When excessive cabin altitude is sensed, the switch closes and provides 28VDC to the control solenoid (horizontal silver barrel) of the cabin oxygen valve. A crew activated manual cable can be seen attached to the aft side of the valve.

Several methods of testing are mentioned in the Maintenance Manual. One of which is testing the switch while still connected to the aircraft, which seemed difficult to almost impossible. Another method allowed for the switch to be removed and tested separately.

A test chamber is required. The switch is attached to some internal wires and placed inside the chamber which is then sealed. A vacuum can be applied via a feed-though AN fitting. With the proper altitude simulated, the switch will close. Continuity can be read with a meter attached to the chamber's test wires.

Actual mask deployment can be verified by jumping the aircraft side switch wiring. The valve solenoid can be clearly heard activating. (I found a broken suppression diode on this particular aircraft.

King Air 200
AMM 35-20-01
WDM 35-20-01-01
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]]> (Mark) kunena Wed, 20 Jun 2018 01:07:40 +0000
Mark created a new forum post in ATA 25 Equipment/Furnishings
Simple issue, but it can be quite a pain pulling up floor panels when these locks are not installed correctly.

By sufficiently turning the fastener counter-clockwise, the tab will swing in "under" the floor support structure and it can be pulled tight in the clockwise direction. Each fastener should have a gap around a 1/4" before the panel is placed back in position for re-install.

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]]> (Mark) kunena Wed, 20 Jun 2018 00:16:53 +0000
Mark created a new forum post in ATA 34 Navigation
A quick video explaining the "crossbleed" function of a Pitot/Static Box. Airspeed indication uses both ram air pressure and static pressure for indication. Increasing altitude while leaving pitot at ambient will cause the airspeed to rise. Opening the crossbleed (which ports static air to the pitot side, keeps the relative difference between the two systems at 0 and the airspeed will not react to increasing static vacuum while going to higher altitudes.

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]]> (Mark) kunena Tue, 19 Jun 2018 00:00:34 +0000
amo4869 just registered on the site (amo4869) profiles Sat, 16 Jun 2018 14:38:16 +0000