Archive for April, 2009

CBs – No reset!

Wednesday, April 29th, 2009

Let’s discuss circuit breakers (CB). We routinely verify during the prestart check that they are pushed in or appropriately disabled. Most of the time this is perfunctory and it’s a boring topic – sorry. Read on.

In the recent landmark accident CBs and wiring were implicated. Note that the rules regarding CBs have changed – In years past, if a CB popped the practice was to let it cool and reset ONCE on the theory that it might be a transient fault. No more. If a CB pops, unless it’s flight critical, do NOT reset. There have been only a few instances of big in-flight electrical fires where the aircraft and lives were lost. In this case, the tab was about $20 million and the lawsuits are flying. Seems like a lot for a simple thermal-mechanical device.

If you smell burning insulation before disabling the appropriate CB, the aircraft should be grounded until the fault has been isolated and the affected wiring replaced. That’s probably going to be expensive. But, if that seems harsh, according to NTSB engineers, once the wiring is hot enough to melt insulation so you can smell it – the insulation is toast, if you’ll pardon the pun. It will no longer function as intended and there is a fair chance that other circuits or equipment may malfunction and cause a fire when you least need it. Don’t forget that on-board fire extinguisher – this is potentially an extremely serious fault. Remember where it is? Can you reach it? Is it properly charged? Again – boring but critical.

Wiring is like props – we take them for granted and they routinely perform with little complaint until something unfortunate happens suddenly. Also suggested reading is ASF’s new In-Flight Electrical Fires Safety Brief on the topic. It’s a short read.

If you have a wiring story, please share it. Many others may benefit.

Old Twin , Old Pilot – A Problem?

Wednesday, April 22nd, 2009

It has been a tough year for crashes in “congested” areas as the FAA likes to refer to cities. The latest involved a 1974 Cessna 421B that went down while attempting a return to Ft. Lauderdale Executive (KFXE) airport.

The 80 year old pilot, according to news reports, advised the tower that he was having difficulty. In some respect this accident is quite similar to the Navajo crash that happened in North Las Vegas last summer. Both involved multiengine aircraft that only had one person aboard that suffered an apparent engine failure shortly after takeoff. In both cases the aircraft crashed short of the runway with no ground injuries but a building, aircraft and pilot destroyed.

My usual caveat applies, since we know few details about the accident so anything here is speculative. The local newspaper made much of the fact that the aircraft had two engines and thus should have been able to continue flight. Generally, most twins will remain airborne if the pilot does everything correctly, they aren’t too heavily loaded and the density altitude is such that continued flight is an option.

In this case, the Cessna was light and at sea level but if the pilot did not identify, verify and feather in the proper sequence and promptly, the outcome will be disappointing. I once ran a little experiment in the back of Flight Safety’s C421 simulator. We found that it took the average pilot, without the benefit of recurrent training, about 5 to 7 seconds to start corrective action in an engine-out emergency. After training that time was cut to about 3 seconds.

Twin or single, they have to be flown right. Some say the second engine just takes you to the crash site and that twins have two engines because they need both to stay airborne. You can engage in that debate without my help.

Of interest, is the pilot’s age and the fact that ASF is working with the University of North Dakota to measure how aging affects pilot performance. If you’re interested in volunteering let us know. Now that I’ve kicked over the hornet’s nest on twins and “mature” pilots, understand that good maintenance and genetics play a critical part on how old either pilot or aircraft really are.

Light Sport Breakups

Wednesday, April 15th, 2009

This just in – The NTSB has issued an unusual request to FAA to immediately ground the Zenair CH601XL, a special light sport aircraft (S-LSA) . NTSB identified 6 fatal accidents involving in-flight breakups and resulting in 10 fatalities since 2006. Two of the breakups occurred outside the U.S.

This is a sobering development in the burgeoning LSA market and one that the “special” designation was hoping to address. “Special” means that the aircraft are built in a factory to ASTM consensus design standards (originally American Society for Testing and Materials). This organization was chosen as a simple, less expensive and extensive alternative to FAA certification. A cynic might say that we should stick with tried and true methods. Of course, if that were the case airplanes might not have been invented and I point out that there have been some spectacular failures in FAA-certificated aircraft. Several of the aircraft were kits so there’s a mix between the factory vs. homebuilt and it appears that if the designer’s specs are not followed exactly, bad things can happen.

We need to learn more. NTSB pointed to flutter and control forces as areas of interest. According to NTSB, “The stick force gradient – a measure of the force applied to the control stick and the increase in lift that results – was not uniform throughout the range of motion, particularly at high vertical accelerations or Gs. The lessening of the gradient at high Gs could make the airplane susceptible to being inadvertently over-controlled by the pilot, which could create a condition in which the airplane is stressed beyond its design limits leading to an in-flight structural failure.”

The NTSB does not have the authority to ground the aircraft but the FAA does. Six breakups in seemingly routine flight does not instill confidence so it’s time to get to the facts – quickly and unemotionally.

The safety record of S-LSA aircraft has been reasonable up to this point with no particular aircraft failure modes. ASF has tallied many landing accidents but this seems to relate to pilot skill as opposed to hardware issues.

This a setback for Zenair, and their family of owners and pilots. We encourage a thorough and timely investigation to resolve this.