Thirty-six years ago, this very month, every King Air 200 in existence was grounded by an emergency Airworthiness Directive (AD) on wing bolts. Back then, ADs were sent through the mail. This one had a really short window for compliance; by the time it was received by owners, they had to act very fast if they were going to get their 200 to a shop before the deadline.
I was managing Beech West in Van Nuys, California, (KVNY) at the time. In the previous weeks, I had heard some hints and rumors about a possible AD coming out on wing bolts for the King Air 200s. The facility’s parts department checked availability and found about 20 sets at the factory; we bought them all. Shortly thereafter, the AD hit. Ferry permits were not allowed, and if you didn’t comply in the timeframe specified, your 200 was grounded where it sat. My office staff contacted every 200 customer we had, then using an FAA directory, we reached out to owners of 200s within an hour of flight time to our facility. Many of them scrambled to get their King Air over to Beech West before the deadline. Most people had 24 hours, or less, notice.
As King Airs streamed into the Van Nuys airport, we grabbed every square inch of ramp space we could and lined them up nose-to-tail. It was a memorable sight – like a mini-Oshkosh AirVenture just for 200s! I had never seen so many King Airs in one place before or since.
As I recall, the AD offered two methods of compliance: (1) Replace the wing bolts, nuts and washers; or (2) Remove the bolts, bake them for 23 hours at 350-400ºF, allow them to cool slowly, then perform non-destructive testing (NDT) by eddy current. If the bolts passed the NDT, they were OK.
We started installing the new parts we had on hand. In other cases, we removed bolts and put them through the second method. I had purchased two ovens so we could have more than one batch in process at a time. After baking, the bolts had to cool down in still air, which meant turning the oven off and waiting for them to cool completely before performing the NDT. This method took a couple days.
During that time, the factory called; they wanted to buy back their bolts. I was sympathetic, but the Van Nuys airport was clogged with King Airs. I had no choice but to respectfully refuse the factory’s request and press on with the job at hand.
I don’t remember the exact date, but the AD kicked in at midnight and by 9 or 10 a.m. the next morning, the first 200 was done and ready to go. The tower, having just learned of the AD grounding all King Air 200s, denied permission to take off. I had to explain to the tower what we were doing, and eventually the word got around that 200s out of Van Nuys were in compliance and OK to fly.
Not to Worry
It was a wild and crazy time with that AD, mainly because it happened so suddenly. If you’re wondering whether we found any problems with the hardware we removed, baked and inspected, the answer is no. Furthermore, I never heard that anyone else found any problems either. My recollection is that a cracked nut was found on a 200 somewhere and this emergency AD was a pro-active antidote to a potential problem.
Product manufacturers recall defective merchandise all the time. Such recalls are usually a reaction to the discovery of numerous problems or injuries or worse. This AD, on the other hand, was more akin to preventative maintenance on steroids. In other words, if there might be a problem, this AD would surely nip it in the bud.
Spar Straps
Way back when, there was some concern about wing bolts in the 90 series King Airs, and it was handled in a similar fashion to the 200s. Around that time, Dave Saunders of Avidesign, who had designed spar straps for a variety of aircraft, came up with a spar strap STC for older King Airs (if this sounds familiar, it was discussed in Tom Clements’ article in the December 2015 issue of King Air). It was marketed as an added safety feature and became popular enough to prompt Beech to design their own spar strap for the 90 series. Bear in mind, it was not required equipment, it was an option. There are plenty of 90s, many of them 30 or 40 years old, still flying safely without spar straps.
If your King Air has a spar strap, you are probably acutely aware of it. They are subject to periodic inspections which are labor-intensive. From a maintenance perspective, they are a real pain to deal with, but I have yet to find a way to remove one and “undo” the STC.
Wing Bolt Inspection and Maintenance
Preventative maintenance is vital to all aircraft. Many years ago, news surfaced of a King Air wing bolt that was severely corroded. The 12-month wing bolt lube was added to the inspection regimen and has proven a very effective remedy. Even though wing bolts are now made with inconel instead of steel, lubing the wing bolts every year is a small price to pay for the peace of mind it provides.
The various King Air models have different calendar requirements for inspection and replacement of wing attachment hardware. The inspection (a three-year or five-year occurrence) includes not just the hardware itself, but also the bathtub fittings, counter bores and flat surfaces.
I bring an NDT specialist in for the required eddy current testing during these inspections. We’ve never found an anomaly in all the wing bolt inspections we’ve done over the years, but the NDT guys I work with have their share of horror stories. Whenever they find bad news, it always seems to involve aircraft that have been greatly neglected; and not surprising, the price required to bring things back up to par is a hefty one. Do it right and pay now, or defer it and pay a bunch more later.
In Tension or in Shear?
The wing bolts in older King Airs are “in tension.” Here, the orientation of the bolt is perpendicular to the fuselage and parallel to the leading edge. If you grasped the head of the bolt with one hand, and the nut with your other hand and tried to pull your hands apart as if to stretch the bolt lengthwise, it would be a crude example of a bolt in tension. The maintenance manual is very specific on how the nuts should be torqued because of the stress being placed upon them. Most of the King Airs coming through my shop have wing bolts in tension.
Beech later switched to wing bolts “in shear,” where the orientation of the bolt is parallel to the fuselage. The bolt is clasped with evenly spaced “fingers” that are at 90 degrees to the bolt. I have a collection of old wing bolts in my office. It’s easy to tell the ones in shear because the “fingers” have worn a shiny stripe at even intervals.
All wing bolts, whether in tension or in shear, are subject to periodic replacement. The lower forward bolts are replaced every five or 15 years depending on the King Air model. Lower forwards in shear have a five-year replacement, but also must be replaced any time they are removed, no matter the reason. Wing bolts in the other positions are replaced every 15 years for all King Airs.
Reputation for Safety
Safety has long been a hallmark of the Beechcraft King Air. Their safety record was a key selling point in 1980, as it is today. Proper and prudent operation coupled with good maintenance is a winning combination that will keep any King Air flying for many more years to come.
1 Comment
I would like to Know wich type of special tools are require to remove wing attach bols on C90 series.