BeechTalk - BT

Username Protected · **Posted:** 08 Apr 2025, 10:33

For the Aztec brain trust,
Are any TC'd and STC'd for auto fuel? I've spent considerable time on the Web and I can't seem to drill down on an answer.
Thanks in advance!

Username Protected · **Posted:** 08 Apr 2025, 10:46

While the Aztec's O/IO-540 series engines only need 91 octane, no mogas STC was ever developed for the airframe.

Username Protected · **Posted:** 08 Apr 2025, 12:24

Username Protected wrote:

While the Aztec's O/IO-540 series engines only need 91 octane, no mogas STC was ever developed for the airframe.

apache 235 peterson tried and failed for vapor lock on crossfeed on a hot day

Username Protected · **Posted:** 08 Apr 2025, 12:28

Username Protected wrote:

While the Aztec's O/IO-540 series engines only need 91 octane, no mogas STC was ever developed for the airframe.

all paperwork aside you're saying that standard 250HP IO540's on the Aztec would run fine on 91 octane mogas? I suppose that is a little comforting in the day and age of uncertainty when it comes to 100LL.

Too bad the STC doesn't exist. One could pay for a small DIY fuel trailer pretty quickly with near half price fuel at the home base.

Username Protected · **Posted:** 08 Apr 2025, 12:35

Username Protected wrote:

all paperwork aside you're saying that standard 250HP IO540's on the Aztec would run fine on 91 octane mogas?

No, that's not correct. Many of those engines were certified for the extinct "brown" avgas (91/96). That is NOT the same as 91 AKI mogas.

Username Protected · **Posted:** 12 Apr 2025, 14:05

Username Protected wrote:

Is the hangup at the ACO that you have two different suffix model engines? How do you handle the difference in propeller bolt sizes? on the B2A?

Can you change crank flange prop bolt inserts to convert match both engines as O-320 B3B and have less headaches. Your B2A is not on the TCDS for the Apache.

For thoroughness and accuracy of public record, My O-320B1A has had the propeller flange inserts changed to accommodate the 7/16 bolts so it is the same as the B3B variant. This is done with guidance via Lycoming SL253A. You are also supposed to strike through the “1” on the engine data plate and put a “3” making the engine a B3A. Thought I’d put it out there

Username Protected · **Posted:** 13 Apr 2025, 19:17

I was looking to do a Mogas STC on my Twinkie, it ran fine in my Pitts with the same engine. The problem with the piper twins is there is no fuel return. The engine will be fine, but without the return line you get vapor lock at altitude. Then you just have a really horrible bad day.

Username Protected · **Posted:** 13 Apr 2025, 22:44

Username Protected wrote:

I was looking to do a Mogas STC on my Twinkie, it ran fine in my Pitts with the same engine. The problem with the piper twins is there is no fuel return. The engine will be fine, but without the return line you get vapor lock at altitude. Then you just have a really horrible bad day.

There are no fuel returns on any airplane with a Lycoming engine, single or twin. They're not needed. Only the primitive Continental fuel injection system needs a return line.

Insulating the fuel lines in the engine compartment would solve any boiling issues.

Username Protected · **Posted:** 16 Apr 2025, 13:38

Username Protected wrote:

I was looking to do a Mogas STC on my Twinkie, it ran fine in my Pitts with the same engine. The problem with the piper twins is there is no fuel return. The engine will be fine, but without the return line you get vapor lock at altitude. Then you just have a really horrible bad day.

There are no fuel returns on any airplane with a Lycoming engine, single or twin. They're not needed. Only the primitive Continental fuel injection system needs a return line.

Insulating the fuel lines in the engine compartment would solve any boiling issues.

Username Protected · **Posted:** 17 Apr 2025, 09:57

[/quote]

I had a late 1963 B model Aztec that was one of the first fuel injected Aztecs that IIRC had a fuel return. My Lycoming powered 1963 Twin Commander 500B w/Bendix fuel injection also had a return that when the orifice clogged ran over rich.[/quote]

There are no fuel return lines on any Aztec. Which has one of the simplest and most reliable fuel systems on any twin.

Username Protected · **Posted:** 19 Apr 2025, 14:41

Username Protected wrote:

-check nose gear trunnion for broken or cracked turn stops from exceeding turn limits while towing. If stops are broken check for twist in steering T bar mounted to aft side of trunnion
-you can inspect the two prone areas of the steel frame for rust without pulling the entire interior. Start with removing the large panel behind the nose gear. The areas beneath the door and the emergency exit and the aft lower fittings where the empennage attaches need to be looked at closely.
-check the gear and drag braces for free play while on jacks.
-check gear actuators for pitting, corrosion on housings and for leaks
-check all flex hoses-there are lots of them
-check fuel selectors for clean shut offs and detents if Dukes-Pricy
-function test check crossfeed valve and drain-getting hard to find
-plan on new fuel caps unless it is an F
-you can check powerpak and gear flap functions pretty well with the onboard hand pump. Retract the gear and make sure selector returns to neutral position w/hand pump (same on extension). Check the gear door rigging and leave gear retracted for an extended period. If it sags down then you likely have a powerpak issue or an internal leak in an actuator
-check exhaust for cracks and frozen slip joints-especially crossover connection in front. If the the tail pipe hangar is broken, or slip joints are not free cracks to the stacks will follow.
-check oil cooler mounting-usually repairs on top of repairs unless upgraded to high capacity later system that takes the cooler of of the left rear baffle
-Check fiberglass nose cowls and integrity of connection to bottom cowls
-check AD compliance on flap fittings-commonly pencil whipped
-airframes seldom have any internal corrosion issues.
-good idea to make sure emergency exit can be easily removed-commonly stuck closed.
-check for later style X braced engine mounts that do away with repetitive inspection AD.
-check for cracked engine exhaust ports
-check for sagging lord mounts. Spinners should line up with nose cowls
-check overall condition of baffles and seals-important on an Aztec
-inspect spinners and bulkheads for cracks
-check hydraulic pump for fluid coming out of seal drain hose
-function check heater and check for AD compliance
-on test flight, before extending the gear select gear up. If you feel a bump then the gear was sagging down. The handle should immediately return to neutral with no bump or delay.
-select gear and flaps down simultaneously to ensure gear priority valve is functional. Gear should lock down and handle return to neutral before flaps start down. Can be done in flight or on jacks)
-look at the upper attachment points on the main gear actuators. The sometimes bend from hard landings.
Look at the attach points on the drag brace A frames in the main wheel wells. The holes get elongated and the attach flanges can crack

Would help to know what year model, TTSN and if Turbo or not

One of the things that I forgot to put on this list.

This picture is of the top wing skin that attaches to the upper spar cap and extends inside of the fuselage a few inches. It is fairly common to see the skin stretched and develop fatigue cracks here from the main spar flexing. This one is on an 8,000 hr. F model and there were cracks on both sides.

It is generally only discovered after disassembly but it is possible to inspect with wings on. It would be very difficult to repair and I doubt that it could ever result in a failure but it should be looked at during a prebuy. I would hate to remove and reinstall an Aztec wing. I can’t think of any economically viable repair scheme even with the wing removed.

The Apaches have a completely different and less robust upper spar cap without the top C channel and the forward inboard wing skin does not have the extension. (Last picture)

Username Protected · **Posted:** 22 Apr 2025, 18:44

https://www.facebook.com/share/p/18nV4Y ... tid=wwXIfr

Per the facebook group Garmin looking for another N registered Aztec to complete gfc600 certification work.

The Piper Aztec/Apache thread