The article Why Twins Crash [Safety Analysis, March] calls attention to our industrys continued insistence on attempting to analyze the hazards of flight with one eye blind. Im referring to the inexplicable failure to institute a simple method of determining the number of hours we actually fly each year.
For some time I have been attempting, without success, to advance an idea (someone else had) whose time is long overdue. Were mechanics required to send in a post card after each annual inspection detailing the make and model of the airplane and its hours flown, anyone else with an interest would have accurate data on the number of hours flown by each type of aircraft in the fleet.
What good is it to attempt to create an accident rate, which is, after all, a fraction, when we are certain only of the numerator (the number of wrecks), but not the denominator (the number of hours flown until those aircraft wrecked)?
I have heard several objections to this proposal, including privacy. But this information concerns the fleet of aircraft and reveals nothing about any pilot. Others raise the specter of user fees, apparently believing that if the government knows how much we fly, it will tax us for using its air. However I have never heard anyone predict that the feds intend to tax flight itself, but rather the use of ATC and weather services, which have nothing to do with hours flown in general.
No large federal bureaucracy needs to be created to develop this information. Rather whoever currently inputs our imprecise data on hours flown, currently divined from fuel sales and pilot surveys, would receive accurate data to put into the federal number crunching apparatus.
The cynic in me suspects that, just maybe, some folks do not want to know how many hours we actually fly, fearing that the number is really much smaller than the current estimate, thereby making the accident rate per hour much higher and demonstrating that we are, as a group, not getting the job of aviation safety done. Do ya think?
Looks like weve finally come across someone more cynical than we are.
Shortcut or Tourist Trap?
Pat Veillettes article Airspace Blunders [Risk Management, March] hits home.
I am an 18-year VFR pilot who spent most of those years tooling around skies in the Midwest. I have been in California since 1998. What a difference!As I was reading the article, I kept thinking back to a recent flight into Santa Monica, and sure enough, Mr. Veillette brought up that hornets nest in the story.
Ive become comfortable flying in the West using flight following, and regularly drop into the L.A. Basin, Las Vegas McCarren or Henderson Muni, and through San Franciscos Bravo airspace. I find the controllers very helpful, and not at all averse to dealing with me VFR (probably because I sound like I know what Im doing on the radio, and I do).
On my first trip into Santa Monica, I was concerned with my exit out of that very busy place. I looked for information at the field for what to expect upon departure and found nothing. I asked the gentleman sitting in the noise abatement office if he had any ideas. He suggested asking the tower controller, and so I did. The controller simply told me to follow the published guidelines in the directories. I already had reviewed those, and that was fine for getting me to the pier, but then what?
As I approached the pier, I was told, cleared to the Sepulveda Pass, contact SoCal Approach by a rapid-fire tower controller who sounded like he had a wad of chewing tobacco in his mouth. I know the pass but just couldnt understand his words, so I had to ask for him to repeat it. Busy controllers usually dont like that, and this one was no different. After two or three back-and-forths, I got the message and headed for the 405 northbound out of the valley. After that, it was a piece of cake.
Pilots unfamiliar with busy airspace and on their first flight into a field need all the help they can get. If Im unfamiliar I tell controllers that upfront. But neophytes should know that once theyve been into a field, the procedures are often repeated each time you do it, and the flights following become a little less stressful as a result.
Sure, busy airspace gets my adrenaline running, but thats one of the thrills of flying. I wouldnt have it any other way.
-Gregg K. Knowles
Wetter is Better
As a subscriber to your fine publication I have often wondered why you have never mentioned the fact that wet vacuum pumps are much safer to use than dry vacuum pumps.
I have had two catastrophic vacuum pump failures while in the clag. Both of these failures were with dry vacuum pumps. I have never had a catastrophic failure with a wet pump, nor have I ever talked to anybody who did.
The wet pumps are no more expensive to buy, or rebuild, than the dry pumps. Wet pumps last for thousands of hours and only slowly degrade in performance. I am not sure why the airplane manufacturers switched to dry pumps, but it has cost a lot of lives. I am a CFII and work my students hard on partial panel, because most of them fly with the dry pumps.
I would be interested to know why the industry supports using the dry pumps when there is a safer alternative available.
-Richard C. Arnold
There is an abundance of anecdotal evidence supporting the position that wet pumps are more reliable than dry pumps. However, theyre not without their downsides, notably the additional weight/complexity of the installation and the fact that they blow out a fine mist of oil.
We suspect that dry pumps come from the same source as cheap plastic interior panels: the quest by manufacturers to save weight wherever possible to boost the all-important useful load number.
Vac System Plan B
After considering the consequences of a vacuum failure in our Cardinal, my co-owner and I have settled on a short-term solution that reduces our risk.
A vacuum failure warning light from Precise Flight was installed that will greatly reduce the vacuum failure recognition time. Then, instead of hand-flying via partial panel, we would engage the Century I autopilot, which uses the electric turn coordinator as its primary sensing device. The autopilot is coupled to the nav or Loran for navigation. The HSI display on a panel-mounted GPS replaces the failed DG for heading information.
Also, our vacuum pump is over 1,300 hours old. We are planning to replace it rather than letting it go until failure to avoid carbon vane debris in the system when it fails. Feel free to shoot holes in either of these strategies.
We think this is a workable short-term solution. You might want to consider, as a long-term measure, adding a backup vac system or an electric attitude indicator. Our preference would be for the latter, because it gives you a backup for both the vac system and the attitude gyro. GPS heading info is a reasonable alternative to the DG.
As for a pre-emptive vac pump replacement, wed recommend that now. After 1,300 hours, youre living on borrowed time.
Low Air Mean Longer Rolls?
I thought I read somewhere that mildly underinflated tires had big effects on takeoff performance in GA planes, but Ive never been able to find any reference to this again. Do you guys have some info?
Your question implies youre curious about the airplane taking longer to accelerate if the tires are underinflated. We have no direct information about the relationship between tire inflation and takeoff roll, although weve heard numbers on the order of 15 percent longer takeoff runs with mildly under-inflated tires.
Theres another danger involved, too. John Lowerys book Professional Pilot points out that underinflation leads to the tire sidewalls flexing excessively. The result is much like working a wire back and forth – premature failure. While the tire may not fail on that flight, the damage is done, setting the stage for a blowout on subsequent flights. The hazard is greater with hotter temperatures.
We Dont Need No Stinkin Climb
You state in your report on twin safety, [Safety Anaylsis, March] that (a)t max gross weight, every GA twin made is supposed to be able to climb on a single engine.
Page 1-3 of The Complete Multi-Engine Pilot, by Bob Gardner, states that (t)he FAA doesnt require that a multi-engine airplane weighing less than 6,000 pounds be able to climb or even maintain altitude on one engine; its only requirement is that the plane be controllable as it gradually sinks earthward.
You (and Gardner) are right that FAR 23.67 does not require a light twin to climb on one engine, only that the manufacturer determines what the climb gradient is (even if its negative). However, every light twin were aware of claims a positive rate of climb when the airplane is below the single-engine service ceiling, which in some light twins is pretty low – 3,800 feet msl for the Piper Seminole, for example.
Of course, just because the book says its so doesnt mean youll be able to do it, too.
Bill Kershner reports in The Advanced Pilots Flight Manual that a study of 11 light twins showed the single-engine, sea-level, max weight climb rates were between 10 percent and 22 percent of the two-engine climb rates. The average was 16.5 percent.