Duplicate Inspection – Flight Controls VIII

The Previous post would have highlighted that sheer negligence has the potential of creating disaster, of devastating proportions. So what can we do to prevent such a thing from happening? Besides stringent quality audits and the use of technology (again!), most civil aviation regulators have come up with a provision in their civil airworthiness requirements, to have flight control systems checked a second time (duplicate inspection) if they have been disturbed in any way during routine or non-routine maintenance. Essentially this means that once a task associated with flight controls is completed, a different engineer/mechanic/inspector will ensure the systems is rigged correctly, and certify the same in the maintenance log book with his/her signature. Kind of like taking-a-second-opinion.
This ensures that if indeed a person did somehow rig the system incorrectly, it can be caught out by a second (likely more qualified/experienced) ‘set-of-eyes’. As I’ve mentioned earlier, control system rigging is not an easy task. It requires a person working in a sometimes very physically constrained environment, with not the best lighting, not the greatest ventilation, and not the best angles of vision (sometimes inverted!). Add to it a whole bunch of cables with several other teeny-weeny bits of equipment, fluid hoses/tubing and wires surrounding the work area, and you have a readymade curry of errors waiting to happen! Not to mention the humongous degrees of patience required from the person working on the system. Speaking of patience, I have personally had the not-so-good experience of holding onto the lamp illuminating the work area of a cable tension setting job, and shifting a tiny bit to relieve a sore bum, only to have my engineer sit up, grab the lamp, and tell me to get the hell out of there!...and send someone else!!

So, it is a tough job, and I think I have successfully convinced you about that!

That also satisfies the claim that making error’s with the flight control system is not difficult.
Duplicate Inspection does alleviate this possibility to a large extent. But there have still been errors; just like the one pointed out earlier. So why does that happen?
Well, the answer to that may be a simple “complacency” issue to a slightly less-than-simple “complex/advanced/digital technology” which can confuse the daylights out of a slightly older generation person!
Having said that, things are being made “easier-to-grasp” nowadays and there is supplemental training all personnel are provided to cover the latest technologies. However, the complacency factor still exists. One thing, though, that can be completely avoided is inspectors “pencil-whipping” an item without a detailed examination!
More on complacency in the following posts.

“You have ...Power!” - Flight Controls VII

We spoke about human error last time around. Now with regard to human error, before I give the impression of finger-pointing the FBW, I want to clarify that human error is applicable equally to both the FBW and control cable systems. This means that it is as easy to make mistakes rigging flight control systems on both types. It’s a difficult task, maintenance-vise to rig and fine tune these systems. The FBW’s today have something called a Built In Test Equipment (BITE) that checks for system malfunctions and gives a reasonably accurate error indication and sometimes locations of malfunctions and equipment requiring attention. However, one still needs to get all the plugs in the right sockets! Figuratively speaking? Not really.

Here’s a story of how things nearly got out of hand.
"Two Maintenance Mistakes Reveal Similar Systemic Shortcomings"

It was a result of cross-wiring the Captains side-stick. That is, a right Aileron ‘up’ command actually led to the left aileron going up, and vice versa. Something that should have been caught out at some stage? Well, at the least during the Preflight? Well, this one escaped all safety nets, and brought a wing tip within 5 feet of the ground!
Again, I’d hasten to add that cable control systems have been cross rigged on many occasions as well. It’s just that in a FBW system, given the advanced nature of the systems, back-ups, error indications, and what not, we should be able to prevent something like this. Something as basic as this!
Maybe it’s easier to get complacent when you have technology of the type available today, to back you up? Maybe. My view of it is that technology can and should be used; but more so as an aid. If we fail to connect our plugs in the right sockets, and to read what technology is telling us, we are not only failing to make use of that technology, but we are arming it (in the true sense of the word) to take away from us, the power we gave it, ENTIRELY!
Until the next time you hear - “You have control” – Fly Safe

Advantages and Dis. - The FBW system - Flight Controls VI

The Fly-by-wire(FBW) concept we discussed earlier, has several advantages over the cable systems. Amongst a few of them, fewer movable components, lesser wear and tear, as a result lesser maintenance; greater precision in control surface movement (via digital input/output), and providing a better interface with other aircraft (and engine) systems, including the Automatic flight control/director systems (what we ordinarily call AutoPilot). The FBW also lends itself to incorporating backup systems and providing what is in technical parlance called, Failsafe systems. Example: If there is a malfunction(say in the hydraulic system), there will be an automatic shift to a standby system and an indication of this in the cockpit. Alternatively there could be a complete systems shutdown and a transfer of control to the pilot. There’s backup!
The primary advantages, though, are greater efficiency and weight saving. These feature most commonly in airline and aircraft manufacturers decisions to shift to the fly-by-wire system.
Now, there are disadvantages too. The main amongst them being those associated with any other electrical systems such as short circuits, system overload and some other more predictable and therefore more controllable factors such as heat buildup, electromagnetic interference etc.
These were some advantages and disadvantages.

In the next write up, we’ll talk about how human error can outdo the best of systems- in our case the FBW system.