Letters 04/99

Avidynes View
As one of the featured vendors, we at Avidyne read with great interest Gary Picous article in the October issue (Radical or retro: The Avionics Crystal Ball Reveals No Easy Answers). Were glad that Picou chose to feature Avidyne as the leader in providing what he identified as the more innovative, leading-edge approach to flight situation display technology.

While we agree with many of the points he makes, we have to disagree with three statements about our technology and our approach: Picou states that developing a certifiable installation will probably be easier for a GNS 430 than for an Avidyne system.

Not so. Both companies provide a very similar basis for installation into aircraft. Both systems are manufactured under multiple FAA TSOs and provide one or more STCs to guide the installer in preparing the installation for signoff by the FAA. In fact, FAA guidelines require a somewhat higher amount of work to install a system with the type of GPS functions provided by the Garmin unit.

Installation and certification of the Avidyne will require loads of paperwork. We completely disagree with this assumption. Any certified system requires approximately the same amount of work to install. The Avidyne system comes with the supporting information that makes installation signoff straightforward.

In fact, because one of our basic design criterions is that the Avidyne FSDs capabilities are expandable through software updates, weve developed the system to be easily removed, upgraded and re-installed.

Wed never trust it on a dark and stormy night, (regarding the Windows NT technology in the Avidyne FSD). We could fill pages with the specifics of why the underlying software technology of the Avidyne FSD is bulletproof. It could be the subject of an entire article. In fact, it should be. But here are just a couple of important points:

First, both the Avidyne and the Garmin systems have the same level of FAA certification. It is extremely unlikely, given the certification process, that either system might crash. Our experience with hundreds of Avidyne FSD units is that they are amazingly reliable.

Second, you cant generalize an experience you may have had running a Windows application on a PC and say that this means its an unreliable operating system for avionics. Ive spent most of my professional life in the computing and software business. I know from experience that most system crashes happen when users are trying to use incompatible applications, or obsolete versions of applications that no longer match the revision level of the operating system.

The Avidyne FSD offers a restricted and carefully matched set of capabilities that are always in sync with the underlying operating system. PC operating systems must address thousands of permutations of devices, networks and applications. This can cause problems. Our FSD provides four or five carefully matched capabilities that are always in synch with the operating system.

Modern electronic systems are amazingly reliable and Avidynes system is no exception. Avidyne provides unique situational awareness capabilities and any pilot who has flown with the system (myself included) realizes that the addition of an Avidyne system makes flying on a dark and stormy night much safer.

Dan Schwinn, President
Avidyne Corporation
Lexington, Massachusetts

While it may be true that the Avidyne system is certified, that doesnt put it in the same category as the Garmin GNS 430 and other IFR-certified standalone boxes, in our view. These mapcom navigators meet TSO C129 and, in the case of the 430, eventually TSO C146, the follow-on for WAAS approval. They can thus serve as primary navigators and the basis for removing conventional navcoms, a distinction the Avidyne system cant yet claim, despite its high price tag.

As for being safer on a dark and stormy night, we agree that the Avidynes moving map display is a terrific adjunct to situation awareness. However, until it has been in the field for awhile and reliability claims have been proven by actual experience, we remain skeptical.

Were also not convinced that new color displays-including the Garmin 430s-will prove trouble free. Only field experience will tell. But on balance, we doubt that a cockpit PC running Windows NT will prove as bulletproof as a self-contained box TSOd as a primary navigator. Were willing to be convinced, however.

Retread Worries
I just read the article about using retreaded tires in your recent Buyers Guide. Im very interested in these savings. However, the POH for my 1978 Bonanza V35B specifically recommends against the use of retreads (as have several trusted mechanics) due to the possibility of swelling from heat buildup during the takeoff run. The increased size would damage the gear retraction mechanism. Comments?

K.R. Grossman
via e-mail

A&Ps vary on whether retreads are a good idea for retractables. But the issue of swelling and/or size is a red herring, in our view. Retreads must meet the same certification requirements as new tires do, including tread pattern and overall size.

One reason mechanics tend to overlook retreads is that the sales margin on them is not as high as on new tires. Since most customers don’t insist on retreads, the mechanics recommendation to buy new is usually accepted.

A36 Notes

There is one correction and one clarification I feel is needed in the article, Six Place Step-Up (January 1999), as it concerns the Beech Bonanza A36.

First the clarification. The author states that the cabin was moved forward which is similar to the way in which Larry Ball in his book, Those Incomparable Bonanzas, describes the design change that differentiated the Model 36 from the Models 33 and 35 Bonanza.

The cabin was moved 10 inches forward on the wing of the A36. This critical movement of the wing in relation to the cabin is the major contributor to a much more forgiving CG envelope.

Next a correction: The first A36 to have a real dual control yoke was the 1984 model, not in 1980 as reported. The 1984 A36 incorporated many new advancements-TCM IO-550 (300 HP), turbine engine gauges and improved aileron response in the stall.

Baggage storage is a worrisome problem in the A36. Even with the sixth seat removed, as the article suggests, there’s still the problem of restraining baggage that shares the cabin with passengers. The small area aft of the fifth and sixth seats is limited to 70 pounds and has a restraining net.

My A36 was not yet five years old when I purchased it, but did not come with the large cargo/baggage restraining net that the original equipment list showed had been delivered with the airplane. A check with Raytheons parts outlet revealed that a new replacement net would cost a whopping $900.

My solution was to remove the fifth and sixth seats and the writing desk. Then I turned the third and fourth seats to face forward, leaving the entire rear area to be used as baggage space with the large baggage net restraining whatever is carried there. There is ample leg room for the rear seat occupants in this configuration unless you have basketball players as passengers.

My airplane is so lavishly equipped with avionics and air conditioning that to carry four normal adults (not 170 pounders, but two 190- to 200-pound men and two 160-pound wives) and no baggage, its necessary to leave 20 gallons of gas behind. There is, however, no CG problem as there would have been in my F33A. Even with these limitations I am still very pleased with my A36 Bonanza.

Bill Pappy
Gainesville, Georgia

TCM Cylinders
You asked for comments on Continental cylinders. I report the following based on 16 years with a pressurized Baron with TSIO-520s: My climb, usually to flight level 250 was at 34 inches/2400 RPM. My cruise was always at 30 inches/2200 RPM. My oil consumption was one quart per 10 to 12 hours. I used Phillips 20W-50 in the winter and 25W-60 during the summer.

I have always cruised and climbed at high manifold pressure to seat the rings against the cylinder walls. This has worked for TCM IO-520s from 1968 to 1994 in a Bonanza and a C-55 Baron, plus the P-Baron.

Unfortunately, in our Cessna 210L with a similar IO-520, the engine used about one quart per three hours. This applied to several engines in that airplane; the original, an overhaul, a factory reman and a top overhaul with new cylinders.

Why the difference? I don’t know. The 210 was operated at about 7000 feet at wide open throttle. The C-Baron was operated at 9000 to 13,000 feet, also at wide open throttle.

Louis Capozzoli
Baton Rouge, Louisiana