Tech Forums

Vacuum anchor technology
I read with interest the article in the March 2008 issue page 32 about the “technology developed to protect mechanics and aircraft” by Tim Maroushek. Although I am concerned about the mechs’ safety, I am questioning what effect the vacuum anchor has on composite aircraft skins. Would the vacuum applied be serious enough to cause local delamination of composite aircraft skins, which as we already know is very difficult to spot and may go undetected. I only hope that enough research has gone in this “new technology.”
— Peter Hartman, Nanaimo, BC, Canada

Qantas article
Mischievous aircraft maintenance reports I expect from the general media, but not from a publication such as yours. In your March edition you report that Qantas serviced 175 aircraft with nitrogen instead of oxygen, putting many flight crews at risk. As I work with the person that carried out this particular mistake, I would like to report the true facts of the incident: Only one aircraft was serviced with nitrogen and as the person was disconnecting the servicing cart, he realized his error. The crew oxygen bottle was replaced before flight, and at no time did an aircraft fly with an oxygen system serviced with nitrogen. Also the carts were not identical as you suggest, but were marked differently. To sensationalize this by your publication only reinforces the reluctance of people to report such matters, when they are blown out of all proportion. I hope there is more research done on the rest of your articles, and I suppose the general media will pick up your article as fact. Lift your game guys. Hope to see some big articles next month on some major U.S. airlines with a lot of assumptions as you have taken the liberty to do this month.
— Andrew Madsen, Australia

Bill O’Brien: I took information for the “Bad Air” article from news reports. I also researched Australia publications as well, as some of them I listed below. If you pull them up you will find that I stayed true to the published reports.

I also want to explain to mechanics just what might have happened if the error went undetected. Many mechanics do not know that the cockpit oxygen bottle is used just about on every flight and is not just there in case of an emergency.

I did not want to put Qantas or their mechanics (engineers) in a bad light and said so in the article. Qantas has the best safety record in the world. The purpose of the article was to point out that even the best organizations have human factor problems. Remember, it was Qantas engineers who swapped the oxygen fittings to the nitrogen cart hoses to service oxygen bottles with Bad Air.

As I said this mistake will be remembered as a classic human factors incident. Thank God no one was hurt. If I find a similar problem on U.S. aircraft, you can be sure that I am not shy about sharing that information with mechanics.

  1. Av Web: Dec. 15, 2007; Nitrogen used to fill Oxygen systems by Russ Niles
  2. The Age.com.au; Probe after Qantas pumps wrong gas into jets
  3. Snich.com Au; Fatal gas pumped into Qantas Jets
  4. PAMA, Dec. 16, 2007 Quantas pumps Nitrogen into jets emergency ox carts

Nitrogen in the oxygen tanks
I have a comment to make on the article (Fine Print, March 2008) about putting nitrogen into the oxygen tanks. Please be advised that hypoxia begins around ~16 percent O2 @ 1 atmosphere (sea level). The tanks would have to be diluted to ~18 percent or less O2 in a pressurized cabin to have hypoxic effects. Now if the cabin loses pressure then it is a whole new ball game as mix and altitude have to be calculated. However it is still a problem that this happened in the first place and that it took 10 months for anyone to find out.
— Terry W. Hall

Digital wiring
I would like to find out more information from Jim Sparks. I read his article on digital wiring in the latest issue and it interests me greatly. I need to receive more training in this area, is there a book he would recommend, or a class that can be attended?
— John Williams

Jim Sparks: I have not as yet found a one-stop complete source regarding installation, maintenance, and troubleshooting for aviation digital communications. Most computer protocol used in aircraft today has evolved from home and office networks. It has been my observation that most information regarding bus installation in the airframe is tribal knowledge and is passed on from one technician to another.

Check out the National Center for Aircraft Technician Training (NCATT), www.ncatt.org. It has developed a standard for an Aircraft Electronics Technician (AET) certification. Its website contains lesson plans which presents the fundamentals to understanding the workings of modern electronic systems.

One of the things my flight department has done is to contact our local A&P school and requested they develop a curriculum around the NCATT standard for our technicians. We bring their instructors in once or twice a week around our aircraft workload. Many community colleges also offer electronics/computer technology courses that may be a good starting point.

Several airframe manufacturers have produced in-depth standard practices for wiring and electronic components that is not easy reading but can be a good source to help with installation and some troubleshooting.

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