Now that I have the Instrument, it’s time for a bit of maintenance. The copilot side door on the Sundowner has hinge leaves
broken both top and bottom. A pair of new MIL-spec hinges is on hand. The IA has signed up to Supervise & Sign. A quick question:
Does one remove the door by popping out the hinge pin and set it aside, before removing the hinge rivets? If so, how? I’m imagining a small piece of hinge stock converted into a pin punch, to pop the pin out to where one can grab it with a pair of vise-grips. OTOH, the door doesn’t weigh THAT much.
Hmm, as a shortcut, one could always just cut off a few more leaves from the existing hinge with a Dremel….
Below is a paste of the NAS40 Hinge specifications overview that is available on the BAC website. All the 19/23/24 planes I have seen, that still have the original piano hinge on the doors, have extruded NAS40 hinge. This hinge is significantly stronger than the later MS-style hinge. The NAS40 hinge has a wider and thicker leaf that will not mate with the later MS hinge, though you can use the MS hinge wire with the NAS40 hinge stock.
If you have broken leafs only on one side of the hinge, and if you can get mating NAS40 stock, you can just change the side that is broken. CAUTION! For many years now, if you order replacement hinge parts from Beech for these applications, what they send is the proper shape to mate with the original extruded NAS40 stock; but it is the much cheaper and weaker rolled hinge. I still haven’t received any engineering support from them that documents the use of the weaker hinge, just because it has the Beech part number on it.
Also please note that the Stabilator has MS hinge through the center section, but that the outer six inches on each end consists of the NAS40 hinge. There is an engineering reason for that; the heavier, extruded NAS40 stock better withstands the vibration and balance mass loads at the ends of the Stab anti-servo tab. One long-since retired engineer who worked on the design of these planes, at the Liberal, Kansas, plant, has personally told me that the MS hinge will not provide adequate support on the outboard ends of the Stabilator, if it is used to replace the original hinge.
If you have an A&P-IA who is willing to certify replacement of the door hinges with MS stock, that should be fine. The other option is to determine how much of the hinge really needs replacement. Then view the specs on the BAC website, and contact Genuine Aircraft Hardware on the West Coast (the link is on the BAC website), to see whether they still have some of the hinge you need in stock. It isn’t as cheap as the MS hinge, but it is the proper stuff. If only one half on your door really has broken leafs, it may also save some labor if you get the correct mating replacement hinge. You can use the old half to shape the flange as needed, if any clearance cut-outs are required. If the shop has suitable tools, like angled pin punches and pliers, it usually is not very difficult to get the old hinge out, You can rotate the door until you find the best access for the circumstances.
And to wrap up, it is starting the engine, shutting down the engine, and taxiing the plane, with the doors open, that cause most of the hinge leaf breakage you describe. If at all possible, try to keep the doors shut during these operations.
Specifications for NAS40 extruded aluminum hinge.
This is an obsoleted and now-rare hinge stock that was used on many of the 19/23/24 airframes. It is most commonly seen in the outboard six inches of the stabilator anti-servo tab hinge, and in the cabin door hinges. Note that Beech began servicing replacements with rolled hinge at some point in time. The extruded hinge is preferred, both for strength and durability, but it has become very hard to find. The NAS40 hinge is stronger than the later MS2001 hinge style, due to the thicker body area and wider tab sections. The two styles will not mate. MS20253 hinge wire may be used with NAS40 hinge, but not vice-versa, due to a .001″ difference in wire diameter.