A Flight in a Twin-Engine Piper Seneca

Seneca II (N78SF)

When I heard we had a Piper Seneca II twin-engine plane in our hangar, it needed to return to its home in Rochester, and we were allowed to get instruction in the plane, I volunteered to take an hour of multi-engine instruction time and fly it up to Rochester. I decided to write up the experience of flying it, since I've written few flying tales in recent times.

First, I'll give a little background on myself and the plane, then the preperation that went into the trip, and then describe the relatively brief flight.

The pilot

I've got a multi-engine rating, though I got the rating for the fun and challenge of learning to fly a twin, not with any intention of flying one regularly. It wound up taking a few years to get the rating because the Duchess that the club used for training was rarely around—it was based out of Dunkirk, so there had to be enough people interested in flying it, plus instructor time, weather cooperation, and if possible people willing to fly cross-countries out towards Dunkirk to help defray the cost of the shuttle flights back and forth. I have about 28 hours flying the Duchess, but it's been several years since I last flew it, and Dunkirk no longer has it.

Since my multi training spanned a few years, I had essentially restarted from scratch a number of times, and I found that each time things came back quicker. So, I wasn't as concerned about how rusty I would be. Of course, this would be an instructional flight, so my goal was to learn about flying a different twin than I knew.

The plane

The Duchess is a good multi-trainer. It has good single-engine performance (read: it climb on one engine), it's not too complicated, and is pretty straightforward to operate.

The Seneca (tail-number N78ST) has two turbocharged engines. They put out 200 HP at sea-level and 215 HP at 12,000 feet. (Remember the "high performance endorsement required to fly a plane with more than 200 HP engines? The Mooney's engine is exactly 200 HP, so it doesn't count. I do have an endorsement from one flight in a 235 HP C-182, and I wouldn't be flying the Seneca solo, so it's mostly just a trivia point.)

It is a six place plane, the fuel tanks hold 128 gallons (123 usable) total, and the max gross weight is 4500 pounds.

The N78ST has various other do-dads, like an autopilot, synchrophasers (it automatically synchronizes the RPMs of the two propellers), plus it is certified for "flight into known icing" so it has assorted items for ice protection (hot props, inflatable wing boots, windscrean heater), and assorted avionics. But none of that was important to me.

The club's 152 was up in Rochester, so the plan was to fly up to Rochester in the Seneca and return in the 152. So, the weather had to be good enough for a 152, which is VFR-only. That was just fine for me, given that this was familiarization flight.

The plan

Originally, the timing was going to be tricky because I had friends that were going to be visiting me that day. And then it occurred to me that these were friends from Rochester. So we modified the plan a little. I would fly the Seneca up with David, and then drive back with my friends. That left a seat open in the 152 on the way home, so Derek joined us, since there was plenty of room in the Seneca on the trip to Rochester. Plus, the timing was less important and I didn't have to worry about a slower trip back to Ithaca (and potential weather delays).

Preperation: Book and In-Cockpit Review

A few days before the flight, I spent a little time in the hangar, sitting in the plane in the left seat and looking around at the controls and the instrument panel, to try to familiarize myself with the layout. The basic six instrument layout was the same as in any modern plane, and the power quadrant was the same (from left to right: two throttles, two propeller controls, two mixture controls). The key speed indicators were different than the Duchess. The blue line was 89 KIAS. Red line was 66 KIAS. (More on those later.) White arc, green arc, and yellow arc were different, but they aren't as critical and are easier to manage in flight. The red and blue lines at the bottom of a twin's airspeed indicator are the critical numbers to know, in the same way knowing the best glide speed for a 172 is critical.

Many of the engine gauges were in different places. And instead of having two indicators on one gauge to show the RPMs of the two engines, there were two separate gauges, one located on the lower right side of the left half of the panel, and the other was almost directly under, and obscured by, the yoke. The manifold pressure gauge, which had two needles together in one gauge, was located between them. But the big difference in the MP gauge was the scale. Instead of topping out at 35 inches, a bit above ambient sea-level pressure, this went to 51 inches. Why does it go that much higher? Because it can.

I've never flown a turbocharged plane before.

The turbochargers can produce ambient sea-level pressure up beyond 10,000 feet. That means they can take the thin air up there and compress it to produce pressures similar to sea-level. So the engine isn't bothered by the thin air up there, and full-throttle means full-throttle. That also means that at sea-level, the turbocharger can produce significantly greater than ambient air pressure. While that can score points on the awesome scale, it also means that full-throttle at sea-level can produce pressures that far exceed what the engine can handle. And that is why there are two warning lights in the center of the panel labeled "OVERBOOST"—one for the left engine and one for the right engine. The POH says never to exceed 40 inches of manifold presssure. So unlike on a normally aspirated engine, on takeoff you set the power based on the desired manifold pressure (about 38-39 inches), instead of just opening the throttle completely.

The alternator and engine start controls were in a place that was new to me: next to the left armrest on the left side of the plane.

Two days before the trip, David had loaned me the Seneca's POH (Pilot's Operating Handbook) to read and review. I read over the important numbers, the emergency procedures, the normal procedures, and some of the systems. I wasn't planning to fly it in ice, let alone clouds (IMC), so I didn't focus on the avionics or other systems. Also, the heating system is different than in a single engine plane, since the engines are too far away from the cabin to just duct air around an exhaust shroud by the engine and then send it into the cabin, they have a heating system that burns gas in the tail. I figured I would let David handle that.

One of the times I was training in the Duchess, its heater was "temperamental," which is to say it stopped working after 10 minutes. It tripped a circuit breaker that could only be reset while on the ground, by opening up a panel in the nose of the plane. We had taken off in 0°F (-18°C) weather on the ground with the heat working. It was -20°F (-29°C) aloft, and 10 minutes later when the heat wasn't working, we were starting to get rather cold. From my sample size of one, I concluded that I shouldn't trust heaters on twins. (Try driving in a car with -20°F air blowing in for 15 minutes and see how pleasant that is...)

A number of the gizmos were inoperative (autopilot, synchrophasers, Mode C in the transponder). None were critical for our flight.

Pre-flight Planning

Saturday morning I arrived at the club. David told me to review some of the basic performance numbers and do weight and balance and accelerate-stop calculations and he would preflight the plane.

It had been flown about 1.5 hours since refueling, and there would be three of us in the plane. A rough estimate put us at 4100 pounds, still 400 pounds under the 4500 max gross weight for the plane. Similarly, we were well inside the balance envelope.

It was a cold morning, around 15°F (-9°C). We were off the charts in terms of performance, in a good way. The best I could do for the accelerate- stop distance was "under 2300 feet" because the temperature was so far below standard. Piper provided no accelerate-go chart, but based on the normal takeoff run (1800 feet), the accelerate-stop, and the almost 7000 foot runway, it was not going to be a problem.

David and Derek returned from the preflight, and I revied my calculations with David, along with briefing the takeoff and landing procedures and reviewing some of the critical speeds. Then I got in the plane so I could once again familiarize myself with the cockpit layout while they pulled the plane out with the tractor. The electric engine heaters had been plugged in all night, and there was a small space heater David had just put in the plane, plugged in, warming up the inside. It was quite pleasant. David pulled the plane out of the IDI hangar using the tractor. We forgot to unplug the space heater, so it unplugged itself with a <sproing!>, but no damage. Then Derek and David got in the plane and it was time to start the engines.

Engine Start

The Seneca starter controls are different from the Duchess' controls, but the idea is the same. Prime it, then crank. Because it was cold out, additional priming might be needed when the engine first starts before it starts running smoothly.

We selected the left engine to start first. We primed, we cranked, it caught for a stroke, then nothing. We tried again. Nothing. Again. One firing, then nothing. And again. After the first two tries, David had taken over trying to coax the engine to life. He primed it more. He tried a flooded engine start. He tried a few things. Nothing worked. After about a minute of trying, we took a break from the left engine to give the starter some time to cool off. We tried the right engine. Prime, crank, and after 1-2 seconds of cranking it started to fire and catch. It coughed once or twice, but extra priming kept it going, and then it started running smoothly. No problem.

After a minute or two we went back to the left engine. It took a few more tries, but eventually it started firing. It almost lost it, but extra priming kept it going, and then it started to run smoothly. We would be able to make the flight!

Taxi and Warm-up

I taxied to the north ramp. The plane would taxi with the two engines idling at 1000 rpm—I didn't have to give it any extra power to start it taxiing, just let up on the brakes. I ran through the checklist. Then we did the engine run-ups. David told me to gently advance the throttles and notice that one throttle (the right?) had to lead the other, and that technique would be needed on takeoff. We verified the two magnetos in the left engine, then cycled the propeller controller, then did the same with the left engine. Then brought the power back so the propellers were running at around 1000 rpm, then did the feather checks, briefly pulling the propeller controller to the feather position for a second, to make sure that system worked. One additional check was to set the RPMs back a little and bring the power up until the governor started to regulate the RPMs. With the engine run-up complete, I called the ground control and requested to taxi for a northwest departure.

Holding short, at the end of the taxiway before Runway 32, we did the takeoff briefing.

Set power to 35" then add a little until it got to 39". This would be around 1/4 of the throttle travel.

Rotate at 71 and set pitch to climb at blueline (89).

After establishing a positive rate of climb, the gear comes up.

After 500 feet, which would come quickly, reduce power back to around 30", RPMs down to 2500, and lower the nose for a cruise climb.

Any problems while on the runway, power comes out and we stop.

If there are engine problems or other series problems while the gear is down, we will gently reduce power and land straight ahead.

If there are engine problems once the gear is up, we're a go, setting the pitch to climb at blue-line.

The airspeed inidicator in a twin engine plane has two additional markings: a blue line and a red line. The blue line is the best single-engine rate of climb (V_y while running on only one engine). That's generally a very good speed to be at when trying to climb, which is what happens when an engine fails when it's not in cruise. Below that is the red line, which is the single engine, minimum controllable airspeed, called V_mc.

In a twin, the biggest concern is what happens when you lose an engine. And the biggest problem comes from trying to get two-engine climb performance out of one engine. A twin will typically hit V_mc, the minimum controllable airspeed when running on one engine, before hitting its V_s stall speed. While both are bad, V_mc involves loss of directional control, as there isn't enough "rudder authority" to stop the yaw, and loss of roll control, as there isn't enough aileron authority to stop the roll. Taking no action means the plane will go inverted and it just gets worse from there. With the weight of the engines fairly far from the center of mass, twin engine planes tend to have a lot of roll inertia. So, once a V_mc roll is developed, recovery from it can be difficult or impossible. So, part of the takeoff briefing in a twin involves explicitly stating the actions to take in the critical first phases of flight if there are engine problems. Having completed the briefing, we were ready to go.

Takeoff, Brief Climb, and Cruise

I advanced the throttles, kind of duck-walking them, once the manifold pressure was in the upper 20s. The engines had a small beat-frequency making the twin sound like a real airplane. We accelerated past red-line and quickly approached V_r. Unlike a Skyhawk that will fly itself off the runway when it's at the right speed, the Seneca required a bit of back pressure to bring the nose up. And then it started climbing. David likes to see the gear come up quickly in a twin. I raised the gear control, and within a few seconds the gear was retracted. I established a fairly high pitch to climb at blue line. Within 5-10 seconds, we were climbing through 500 feet. I brought the power back a bit and then pulled the propeller controllers back some and lowered the nose to establish a cruise climb and we were on our way.

We leveled off at at 3,500', instead of 4,500', because of clouds, so the level-off came pretty quickly. We set the manifold pressure to be around 25", RPM at 2500, and leaned the mixture some, trimmed to lighten the yoke weight and closed the cowl flaps. We weren't going terribly fast, but then I didn't need things to happen that quickly given that there was a lot to get used to in this plane.

The synchrophasers were inoperative, so I had to synchronize the two propellers by hand, as I learned in the Duchess. Get them close, and then make a few small adjustements to one prop control until the beat frequency disappears. It wasn't too hard to do.

We called up Elmira to get flight following to Rochester. Our transponder was showing us around 4,200' or so, about 700 feet higher than we were, so they told us to stop squawking altitude, switch to Mode A and advise them of any altitude changes. David had had problems with Mode C on the transponder on the flight to Ithaca and the plane had had problems with it before. So we knew it was not likely to work. Best to get that sorted out with ATC early in the flight.

At 25" and 2500 RPM, we weren't going terribly fast, Elmira was showing our groundspeed as 135, but at that point, I was content to get used to the plane and its systems without everything happening at the speed of the Mooney rocketing downhill. As David said, "Beer flavor at champagne prices."

With the heavy engines on each wing, I could feel the increased roll inertial; it was much heavier than that of a single engine plane. It took a more aileron input to get the plane to roll. And similarly, once it starts to roll, it takes more aileron force to stop the roll. It's kind of a heavy, truck-like feel.

Flying on One Engine

I had ask David about doing a little single-engine work, to get the sense of how the Senca flies on one engine. So once we were almost over the Canandaigua airport (as an extra measure of safety), David had me retard one of the throttles gently. The Seneca has counter-rotating props, so the yaw from losing either engine is the same, just in the opposite direction (that's not the case if they both spin the same direction, usually that means there's more yaw when the left engine quits). I pulled back the left engine. The plane started to yaw and roll to the left. I applied some rudder (split the ball) and a little aileron and the plane was flying fairly normally. The one thing that was slightly alarming was that the airspeed was bleeding off. We had dropped from around 120 to somewhere in the 90s. Blue line was 89, so that was fine, but I had a strong tendency to want to hold altitude, and at 25" MP, holding altitude means we lose speed to do it.

Without much thought on my part, the plane was getting close to blue line. Red line was another 23 knots below that. And really, those numbers are predicated on the worst-of-all-possible worlds. One of the conditions used to determine V_mc is that the operating engine is sets to maximum available power. We were nowhere near that, so the asymmetric force created by the good engine is much less than what was used to determine the value of V_mc, and the force required by the rudder to counteract the asymmetric thrust is equally reduced. I wasn't concerned about doing a V_mc roll. It was just a wakeup call as to how insidious the problem can be, especially for a pilot who is alone in the plane with a very stressful, busy workload.

After a minute, we slowly brought power back in on the right engine. Since it hadn't been at low power long enough to "shock cool", we didn't have to wait to warm up the engine, as long as we were gentle about bringing power back up.

Shortly after this, ATC called (we had been handed off from Elmira to Rochester) and said, "Seneca 78-Sierra-Tango, waiver for Mode C requirement for class Charlie airspace granted." That caught me by surprise. We hadn't asked for anything. Then it occurred to me that we were flying with no Mode C, since it had been reporting the wrong altitude, and Mode C is required to enter Rochester's airspace. It's not a requirement for Ithaca and all our planes have functioning transponders, so I've never needed to think about it. Rochester knew we were coming because of the flight-following, and initiated it themselves. It also answered my question of how does one get an authorization to enter airspace that requires Mode C. Simply ask, or in our case, just fly towards their airspace. The plane was based in Rochester, so it might have been a familiar call sign as well. David replied to ATC, thanking them and saying that he had been told that the plane would be getting the transponder fixed after this.

Approach, Landing, and Taxiing In

As we got closer to Rochester and the shore of Lake Ontario, the weather was getting a bit worse. Visibility and ceiling were reducing, though it was still way above VFR minimums at the airport. We called Rochester approach and told them we would be decending from 3500 feet to 2000. I lowered the nose and adjusted the trim. We didn't need to pull the power back further yet.

Leveling off at 2000, I then began to reduce the MP to get to approach speeds. Using Mooney power settings as a rough approximation, I set the throttles to 21" and pulled the props back to about 2200. Approach handed us off to tower. We would be landing on runway 25. We would be making a left base entry. It took me a while to spot the airport and runway, but eventually I did. David spotted it much sooner, but he's also flown there more often and more recently than I have.

I started the standard "GUMPS" checklist, with some variations.

Gas: Do NOT turn on boost pumps in this plane.

Undercarriage: Verify the speed was below 125 and lower the gear, check for 3 green lights, and look at the mirror on the left engine nacelle to visually verify the nose gear was down.

Mixture: Full rich.

Propellers: Eventually go to high RPM, but not until the throttle has been reduced more.

Seatbelts: Verify seat-belts (for self and passengers).

At that point David turned off the heater, so it would have a few minutes running only the blower to cool down. I retarded the throttles to about 17" or so and added the first notch of flaps after verifying the speed was in the white arc. With the runway in sight, I turned onto final.

While the Seneca is a stable platform, it requires the pilot to make things happen. I needed a bit of coaching from David in terms of stabilizing the approach and setting the picture. There was a bit of a left crosswind to add to the fun. On final, I was shooting to keep the airspeed at blue line. Then slowly retard the throttles a bit, raise the nose and slow down another 10 knots. Keep it lined up with the runway and heading for the aim point.

I generated some pilot-induced-oscillation until David made me make small corrections, then fly level, then make other small corrections. Eventually things stabilized. We were probably flairing around 70 with appropriate rudder as I closed the throttles and tried to keep the cross-wind correction in.

We touched down with a little bounce. My landings in the Duchess had generally been far smoother. One thing I did right was not rushing anything at that point. It was a +4000' runway and we had a lot of it ahead of us. Once the nose wheel was down and I had the elevator fully back with a crosswind correction in, I gently starated to apply the brakes to get a feel for them, before applying more pressure. We stopped and taxied off with probably 1/3 of the runway remaining.

Taxiing in, David took the controls to maneuver us to the parking spot. We verified everything was off and then shut down the engines. It was 1.0 hours on the Hobbs meter.

Some Wrap-up Thoughts

It's a fun plane. It would be nice if the various avionics worked better and if I fly again, I'd like to take it up to a higher cruise speed, and do a few more takeoffs and landings to get comfortable with it.

I also like to review how a flight went afterwards. The first question is: was it safe? And to be honest, had I been alone, the answer would be no. Having never flown a Seneca and having a few years elapse since I last flew a twin, I was very unfamiliar and rusty. I'd need a few hours to get to know the plane and to improve my skills in it. But that doesn't really bother me, since I wasn't expecting to perform to checkride level. In general, it went OK and it seems like it's a plane that wouldn't be too hard to master.

So the second question is what would I have done differently or learn from the flight? There weren't many significant decisions I made, so most of what I learned would be the areas I need to improve, which is standard skills like takeoffs, landings, general system familiarity. Nothing a few more hours wouldn't fix. At that point, I might be safe to fly solo in certain conditions. But to really master the plane, it seems like I'd need another 20-50 hours flying it. It makes sense that insurance companies generally require a pilot to gain that many hours of duel before they will be covered for solo flight.

Given the cost and how infrequently I fly on long cross-country trips, I'm not looking to use my multi-engine license other than on the occasional flight every year or so for the fun and challenge. But it's a good experience in terms of managing a more complex plane. And having two throttles and engines that pulse out of phase before they're syncrhonized makes it sound and feel like a real airplane.

This page last modified Mar 16, 2013.
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