A flood at the Piper’s Lock Haven facility destroyed the tooling for the Comanche, and Piper Aircraft developed the Seneca as a replacement aircraft for its popular Twin Comanche. Employing “parts bin” engineering and following the marketing strategy of the time, the Seneca is probably most accurately described as a twin-engine Cherokee Six.
The original Seneca, however, was not regarded as a success. Handling problems and poor performance plagued the initial design.
In 1975, Piper introduced the Seneca II. With this aircraft Piper addressed the handling issues found in the original design, but the biggest improvement came from the incorporation of the Continental TSIO-360 engine.
This engine featured a fixed wastegate turbocharger and made the same 200 hp at sea level as the engines on its predecessor, but made 220 hp at 12,000 feet, and maintained 75 percent power all the way to 18,000 feet. The change to a turbocharged engine gave the Seneca II the performance advantage it needed to compete against Cessna and Beech.
The model further evolved as Piper introduced the Seneca III, IV and V. The Seneca V is still in production today, and still uses a variant of the Continental TSIO-360, though now it incorporates a sophisticated absolute pressure controller to manage turbo boost (as opposed to the fixed wastegate on the Seneca II).
The Seneca features aluminum construction and utilizes an electrohydraulic power pack to operate the landing gear.
The stock Seneca II is a really good airplane. Like its Cherokee siblings, the Seneca II is somewhat nose-heavy, and with two on board in the front seats, a full-flap landing results in a very flat landing attitude. It is very stable in both pitch and roll, and it is an excellent instrument platform.
The nose baggage compartment is quite large, but limited to only 100 pounds. However, loading the plane inside the requisite CG range is not a challenge, as the CG range is nearly 12 inches at maximum gross weight. The Seneca II and later models feature a nearly 1,700-pound useful load.
The Seneca II is actually a little faster than the normally aspirated Aztec at altitudes where the turbo doesn’t present an advantage. My Seneca turned in 172 knots at 10,000 feet on 26 gallons gph (13 gallons per side) at a power setting of 30.5 inches of manifold pressure and 2,300 rpm. That translates into 70.5 percent power. Of course, go high, and you would go faster—about three knots per thousand feet faster—all the way up to about 18,000 feet.
The turbochargers do create some engine temperature management issues, and do require a deft hand to manipulate the throttles as your right hand is essentially the absolute pressure controller. It is possible to over-boost the engine, despite the automotive-type, pop off over-boost valve.
The original engines were prone to case cracking, but have been replaced by what is referred to as “heavy case” variants of the Continental TSIO-360 engine.
Details and Mods
Where the Seneca shines in my opinion is in ease of entry and exit for the passengers. The Seneca retains the huge left-side cargo door from the Cherokee Six, making access to the aft seats and cargo area—most of which are club-style (though early Seneca IIs featured all forward facing seats)—a breeze. There is no wing to climb over, no great height to heave your cargo through.
The aft seats are held in with ¼-turn fasteners, making removal a snap and creating a nearly six-foot-long cargo bay. I actually hauled a refrigerator down to a friend’s home in the Bahamas using my Seneca. Getting the refrigerator in and out of the aircraft was no problem.
Air conditioning was a factory option on the Seneca II, and was something you could not get on an Aztec.
But like the Aztec, there are all kinds of STCs available for the Seneca, from one-piece windshields and axial flow cowls, to gap seals, recognition light wingtips and three-blade propellers. Parts are not a problem, and it is no challenge to find a mechanic who knows how to work on one.
The popularity of the design is proven by the fact that it is still in production some 37 years after its introduction.
Seneca II Buyer’s Guide
by John Loughmiller
The Seneca II is probably the biggest bang for the buck there is in light twins right now. Not only are parts available from Piper, it has several design features that help keep the complexity (and therefore, maintenance costs) to a manageable level.
THE SENECA II HAS AN ECONOMICAL DESIGN.
For instance, there are no up-locks to worry about for the landing gear—the retraction system is an electrically operated hydraulic pump that holds the gear in the retract position with pressure alone. This means you don’t have to crank the gear down; just release the pressure and the gear will fall down due to gravity.
The flaps are actuated by a simple Johnson Bar lever, as opposed to an electrical system with position sensors. The turbos’ fixed wastegates require pilot management rather than using an automatic controller; while some may find this feature a hassle, it’s definitely cheaper to maintain.
THE SENECA II HAS A 100-HOUR REQUIRED INSPECTION.
Seneca IIs have a recurrent AD for the nosegear. Every 100 hours, the actuator attachment mounting as well as the actual gear casting must be inspected—which takes about eight hours when done correctly. There is a second part to the AD that requires a stack up assembly to be replaced every 500 hours at a parts cost of around $150 and another five hours or so of labor.
A second recurrent AD involves the Janitrol heater which must have a leak down test done every 24 months. The usual cost is $300 to $500 for the inspection, more if anything is found to be wrong.
There’s also a 100-hour inspection of the heater required by another AD for the fuel shutoff switch.
All the other ADs should have been done some time ago and are not recurrent if done—and logged—properly.
THE SENECA II HAS RANGE AND ROOM.
Operationally, flight plan for 23.5 gph fuel burn at 65 percent power and 160 KIAS (at 10,000 feet). Although the airplane has a service ceiling of 25,000 feet, most operations take place below 12,500 feet.
With standard fuel tanks, you’ll be just shy of four hours to tanks dry, and five hours to tanks dry if the long-range tanks are installed.
My Seneca II has long-range tanks and the unbreakable rule I use is to always be on the ground at the four-hour point (when starting with full tanks), so there’s never a chance of running out of fuel due to overly-optimistic flight planning.
There is a Zero Fuel Restriction, so payload calculations require both a standard weight and balance plot, plus a check to make sure you haven’t violated the placarded limit that shows the weight above which the rest of the load has to be fuel.
Speaking of weight and balance, you’ll often see Senecas with a case of oil riding around in the rear baggage compartment. This is because you can go right through the forward balance limit if you have a heavy pilot or two average-weight people up front and no one seated in the cabin. Without some weight in the rear baggage compartment, you can run out of elevator in the flare and land nosegear-first. This is one reason for the nosegear AD.
THE SENECA II HAS GOOD STOCK AVIONICS.
Most Seneca IIs with no avionics upgrades will have a Century IIIC two-axis autopilot with altitude hold and either King or Collins Nav/Coms. If you can find one with a brace of Garmins, so much the better—but the standard IIIC autopilot is still a good one, although parts are getting tough to find. Because it’s not a rate-based system, it will handle turbulence quite well and can easily handle turns at the marker without overshoot.
The engines on the Seneca II are counter-rotating Continental TSIO-360 and LTSIO-360 models. For 1978 Seneca IIs, you will almost certainly have “EB” series engines installed which have an 1,800-hour TBO (but check anyway, since “E” suffix models have a significantly shorter TBO).
THE SENECA II REQUIRES A PILOT WHO IS A GOOD PLANNER.
Adhere to the two-minute cooldown guidance for the turbos after landing before shutting the engines down if you want the turbos to make TBO. Also, reduce power two inches of manifold pressure at a time, and wait at least a full minute before you make the next two-inch power reduction in the descent. Cracked cylinders from shock cooling can be the result of disregarding this advice.
Patterns are generally flown at 102 KIAS downwind, 92 KIAS base, and across the fence at 80-82 KIAS with full flaps unless the wind suggests otherwise. Gear speeds and flap extension speeds are reasonable but require planning ahead—just as the gradual power reduction requires planning ahead.
Seneca IIs are a bargain right now due to the economy. Search for an airplane with less than 4,000 hours on the airframe, less than 750 hours on the engines, and props that have been overhauled relatively recently. Have a reputable A&P do a pre-purchase inspection for you, and plan on spending around $5,000 to $8,000 for things that were not caught in the inspection.
Finally, you’ll need minimums of 250 hours total time, 100 hours multi-engine time and 25 hours in Senecas to get a reasonable rate on insurance.
Seneca II PA-34T-200
Powerplant: Continental L/TSIO-360-E/200
Wingspan: 38.92 ft
Empty weight: 2,770-2,848 lb
Gross weight: 4,570 lb
Useful load: 1,722-1,800
Max takeoff weight: 4,570 lbs
Fuel capacity: 93 gal usable
Fuel capacity, w/ opt tanks: 123 gal usable
Oil capacity, ea engine: 8 qt
Baggage capacity: 200 lb
Takeoff distance ground roll: 900 ft
Takeoff distance over 50-ft obstacle: 1,240 ft
Rate of climb, sea level: 1,340 fpm
Single-engine ROC, sea level: 225 fpm
Max level speed: 198 kt
Normal cruise, 75%: 191 kt
Economy cruise 55%: 164 kt
Service ceiling: 25,000 ft
Single-engine service ceiling: 13,400 ft
Landing distance over 50-ft obstacle: 1,760-2,090
Landing distance, ground roll: 1,050-1,380
Limiting & Recommended Airspeeds
VMC (min control with critical engine inoperative: 66 KIAS
VX (best angle of climb): 76 KIAS
VY (best rate of climb): 89 KIAS
VNE (never exceed): 195 KIAS
VS1 (stall, clean): 63 KIAS
VSO (stall, in landing configuration): 61 KIAS