Q: Dear Steve,
I fly a Seneca II and so far it’s been a very dependable airplane. But I’m seeing something that I haven’t seen before and wonder if you can give me some information to understand what’s happening.
One of my crew told me that he has seen some blue smoke coming out of the exhaust of the right engine when I first start up. When I asked him to tell me about it, he said the blue smoke was visible for about 10 seconds, then it disappeared. (He didn’t see any blue smoke when I started the left engine.)
He’s been working for me for five years, and is almost always the guy that takes me to the airplane when I have to fly to one of our remote locations. He’s a smart guy, and when he told me that he didn’t remember ever seeing the blue smoke before, I thought I better get some help.
A: Dear Sam,
It sounds like oil is leaking into the hot side of your turbocharger and then being burnt as the turbocharger heats up after starting the engine.
On the outside, aircraft turbochargers look like nothing more than two scroll-like housings joined to a steel center section. There’s a scroll-like housing on the turbine (the exhaust, or “hot”) side of the assembly; and a scroll-like housing on the compressor (the air inlet, or “cold” side) of the assembly.
The turbine wheel and the compressor wheel are mounted on a common shaft that is supported by bearings in the cast-iron center section. The shaft is cooled and lubricated by pressure oil pumped from the engine. Labyrinth seals prevent the lubricating oil from leaking out of the center section.
The turbocharging system that’s installed in your Seneca II is what’s known as pressure relief valve control system. This type of system is used on Seneca IIs, Seneca IIIs and turbocharged versions of the Arrow and Dakota.
This simple system routes all the exhaust gas pressure developed by the engine to two parallel paths: the first path goes to the exhaust turbine, the second path is a bypass path. A restriction in the bypass path is adjusted on the ground by mechanics to produce the proper full throttle critical altitude. This restriction is a fixed wastegate used to control the turbine rpm.
In the case of your Seneca, a properly adjusted system should be capable of producing 39.5 to 40 inches of manifold pressure (at 2,575 rpm and full rich mixture) up to an altitude between 11,500 and 12,500 feet MSL.
This type of turbocharger system is extremely simple but requires constant pilot attention since any throttle movement directly affects boost, and because the inlet air to the engine is always warmed by passage through the turbocharger.
Finally, although the turbocharger itself has the capacity to provide additional boost above the critical altitude, this boost can’t be utilized since the wastegate can’t be adjusted during flight to “get” that boost.
Fortunately, Merlyn Products of Spokane, Wash. has developed Merlyn Black Magic, a wastegate control system that lowers engine temperatures, greatly increases the critical altitude and relieves the angst that revolves around the possibility of overboosting the engine due to accidental or inadvertent throttle mismanagement.
A couple of things can cause smoke upon startup. The easiest (and therefore, the first) thing to check is bearing wear. You can do this by removing the ducting from the inlet-air side of the turbocharger and trying to manually move the shaft.
The shaft must rotate smoothly, but there shouldn’t be any in-and-out or up-and-down movement. Spin the shaft; feel for ease of rotation and wear. Listen for any rubbing sounds.
If the shaft drags, it’s a sign of heavy coking or sludge in the oil cavity. This may have been caused by not changing the oil often enough; not delaying engine shutdown until the turbocharger has cooled down; or a restriction in the oil delivery line. Restricted oil flow will cause overheating in the center section.
While you have the inlet air ducting off, take a good look in the scroll for oil. There shouldn’t be any on the cold side. While you’re at it, get a mirror and a flashlight and inspect the turbine (hot) side for evidence of burned oil.
A weak oil scavenge pump can also cause smoking and leaking check valves in the oil delivery and oil return lines. When the engine isn’t running, these check valves close to prevent oil from flowing under gravity to the center section. If one of these valves isn’t seating fully, oil will creep past the shaft labyrinth seals.
Three Piper Flyer Association supporters—Approved Turbo Components (ATC) Hartzell Engine Technologies (HET) and Main Turbo Inc.—all offer great information about turbocharger systems and troubleshooting on their company websites. (See Resources for the URLs. —Ed.)
ATC’s Knowledge Center includes FAQs, troubleshooting, torque tables and more available as downloadable PDFs.
HET’s Troubleshooting page is in a Q&A format and can give you important details with just a few clicks. Service Information (Service Bulletins, ADs, Service Letters) are also accessible.
Main Turbo’s troubleshooting information is organized by symptom, offering possible causes of trouble and actions for each. The company also offers a maintenance tips newsletter by email subscription.
Q: Hi Steve,
I too fly a Seneca II, and am probably okay since summer is finally here, but I need a new windshield ice plate. My five-year-old dropped it when I wasn’t looking and the glass shattered.
I install the shield as soon as the snow starts to fly in the fall and leave it on until spring. I don’t often have to turn it on, but since I fly all around the Northeast and sometimes into Chicago and Cleveland, I have to be ready for an ice encounter.
What are the options for getting this one repaired? I’ve heard that new ones are hideously expensive. If I have to bite the new-part bullet, I will—but I’d like to know if there are other options.
I also need some guidance on how many times I can patch my wing boots. Every few years we find another hole or two. I know I have to budget for de-icing boot replacement—but I want to know the repair limits, just so I can gauge if it’ll be sooner, or later. Can you help me?
A: Dear Bob,
It’s too bad your son dropped the plate. You have a couple of options.
The Piper part number for your plate is 78148-00. I checked with a Piper parts dealer and these plates are available, but the dealer told me she would have to check with Piper for a lead time. One online site cited a six- to nine-month delivery delay. List price is $5,501.
PFA supporter B/E Aerospace sells windshields for Piper Saratogas, but in talking with Joe Evans, marketing specialist at B/E, if you or any Seneca owners need help securing a replacement plate before winter, the company would be happy to help.
Evans mentioned that you can also get a quote from one of B/E’s installation centers. The link is in Resources at the end of this article.
I found plenty of used plates by typing that part number into an internet search engine, and the majority of the ones I found were listed as “used-serviceable.” Most used parts houses provide a short-term return-if-not-satisfied window; I’d ask before sending your money.
As far as boot replacement, B/E Aerospace has a pneumatic de-icer maintenance manual that provides guidance on evaluating boot condition. (See Resources for the link. —Ed.)
The tests for condition include a time-to-inflate test, a leak test and a time-to-deflate test. Any variation from prescribed times (six seconds to full inflation at regulated pressure; no more than 3 psi pressure loss after 60 seconds with inlet pressure sealed, and no more than 22 seconds to leak down (no vacuum)) indicates a less-than-healthy boot.
The following is from the B/E manual regarding total patch areas:
Recommended limits for application of patches for maximum operating efficiency of a pneumatic de-icer.
Three (3) small patches (1 ¼” x 2 ½”) per any 12-inch square area.
Two (2) medium patches (2 ½” x 5”)
per any 12-inch square area.
One (1) large patch (5” x 10”) per any 12-inch square area.
Additional information about evaluating your boots is listed on the
“10 Reasons to Replace Your Wing Boots” published on the Ice Shield website.
This information should provide some guidance for determining the state of your de-icing boots.
Know your FAR/AIM and check with your mechanic before starting any work.
Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960
Piper Comanche. Send questions and
comments to .
Turbo systems and service
– PFA supporters
Approved Turbo Components, Inc.
Hartzell Engine Technologies
Main Turbo Systems, Inc.
Wastegate control system
Merlyn Products, Inc.
B/E Aerospace, Inc. – PFA supporter
Ice Shield installers
Ice Shield Pneumatic De-Icer,
B/E Report #97-33-047
“10 Reasons to Replace
Your Wing Boots”