Where's the Throttle?

Oh, the difference a year can make!

April 1, 2004

You checked out in a Cessna 172M the first time the United States sent troops to squelch Saddam, so what could be so different about a new model? Well, it's more than the new paint job....

Model differences can be no small matter, especially when the heat's on. Here are some common differences to help you train for the airplane you're in, and to inspire you to get a little instruction when you must accept an older or newer substitute.

A few years, a big difference

Adrian Eichorn, an instructor for the Bonanza/Baron Pilot Proficiency Program, an A&P with inspection authority, and owner of a "showbird" 1962 Beechcraft P35 Bonanza, owns a thick book that lists each model and year of the long-running Bonanza line, and the changes made between each iteration. "You can stand back and look at a Bonanza and they look pretty similar, but you get up close and wow!" says Eichorn.

Yes, those Bonanzas offer wide variety between models and even within a given model from year to year. Case in point: A 1971 A36 varies greatly from one built in 1984. The most obvious difference is the throwover yoke in the older A36. If you plan to fly with another pilot on board, you need to understand the procedure for swapping the yoke, and to practice this performance on the ground before trying it in the air. Also, the throwover yoke poses concern for those wanting to take instruction in the airplane. FAR 61.45 specifies that an airplane used for a practical test must have flight controls "operable in a conventional manner by both pilots" — and that would not include the examiner grabbing fiercely at the yoke's central hub — "unless the examiner determines that the practical test can be conducted safely in the aircraft without the controls being reached." That leaves the question open for an examiner (and by extrapolation, a flight instructor) to decide whether he or she feels comfortable sitting right seat with you during instruction.

A Differences Checklist

  • Read the pilot's operating handbook when you fly a new version of a model you're already checked out in.
  • Note specific differences between the versions, including the large (a carbureted engine instead of a fuel-injected one) and the small (the placement of a switch). Both affect various procedures.
  • Go through the procedures for the airplane, and look for changes resulting from a specific difference. The presence of an electric fuel pump may change the start procedure, affect procedures for switching tanks, and become an immediate action item in the event of an engine power loss.
  • Fly with another pilot or instructor well experienced in that version of the airplane. The Bonanza/Baron Pilot Proficiency Program, for one, attempts to match owners with instructors who either own or specialize in specific versions of the model.

In 1984, Beechcraft reengineered the throttle quadrant on the A36, replacing the vernier throttle, mixture, and propeller controls with levers more like you'd find on a jet. And it rearranged the controls so that they followed a standard pattern, left to right, with the throttle, prop, and mixture. Electrical switches, including lights, avionics master, air-conditioning controls, and the fuel pump, were condensed into one location on the lower pilot-side panel.

However, the placement of gear and flap handles brought the most heartache for early Bonanza owners. These airplanes had similar flap and gear switches, and their position on the panel was reversed from those switches in most retractable-gear airplanes. This gotcha led to instances of pilots raising the gear switch by mistake while taxiing in — when they thought they had retracted the flaps. To compound the issue, earlier models had just one squat switch and it was located on the right main gear. As weight comes off the gear during takeoff the strut extends slightly, closing a circuit and delivering power to the gear motor if the gear switch is selected to retract. While the squat switch prevented the gear from retracting while the airplane was at rest on the ground, the same couldn't be said if the switch was selected to retract while the airplane was taxiing. For example, if the right main gear became unweighted when turning off of the runway onto the taxiway, the gear might come up. Beechcraft addressed the issue by placing a squat switch on each main on newer-model Bonanzas, starting in the mid-1970s.

The gear cycle also got a boost as Beechcraft upgraded the electrical system through the years: "It takes four to five seconds for the motor to raise the gear on a 24-volt system; about nine to 12 seconds on a 12-volt system; and really old ones [generator driven] take 12 to 14 seconds," says Eichorn. "You can sit in the restaurant watching someone take off, see how long it takes the gear to come up, and tell how old the electrical system is."

Prior to 1961, V-tail models had "piano keys" on the panel, including the gear and flap switches; the "modern" panel came on the scene in 1961 in the V-tail, while A36s and Debonairs have always had the next-generation panel. Beechcraft changed the switches, in both position and feel, to resemble those in other retracts. In addition, the older Bonanzas had flap switches that the pilot needed to hold in place in order to deploy to a given position, after which the flap switch popped back into its original aspect. Starting with 1984 models, the flaps have three settings: Up, Approach, and Full; and the pilot can select the setting and leave the actuator in that position. A minor difference, but one that could trip up a pilot who expected full flaps and released the switch only to have them deploy a few degrees and stop.

One twin not like the other

Another model that shows dramatic change among different years is the Piper Seminole (see " Lord of the Light Twins," page 88). Essentially, Seminoles fall into two camps: those built from 1978 through 1982, when production ceased amidst company troubles, and those built in 2001 and after (although the Seminole was back in production in 1988, and deliveries began in earnest in 1995, only a handful were made each year prior to 2000). For simplicity, we'll refer to them as 1979 and 2001 Seminoles.

Airline Transportation Professionals Inc. (ATP) has outlets across the country that specialize in training pilots in accelerated fashion for various checkrides, as well as providing a full curriculum for budding professional pilots. All ATP locations use Seminoles for multiengine training, and the company's instructors go so far as to recommend that an applicant prepare for his or her checkride in either 1979 or 2001 Seminoles, and minimize any cross-over time. The concern is that to teach the differing placement of the ignition, battery and alternator, and fuel pump rocker switches, as well as other electrical equipment switches, would add unwanted time to the program and possibly add to confusion during the stress of a checkride. That's an important thought to keep in mind, even if you aren't training for an additional certificate or rating. An emergency can be stressful, too.

On the 1979 Seminole, most of the electrical switches — including battery, alternator, mags, pumps, starters, and lights — are located on the left side panel. While close to the pilot, there is some awkward twisting involved to manipulate them, especially during engine start, so when the Seminole resumed production in 2001, Piper relocated most of these switches. The mags got plastic guards, the kind that protect the switches from the pilot's knees, also adding a little extra fumble to get to them. But for the most part, the changes make the cockpit work better.

And other Pipers...

While the older Piper Archers seem to have more legroom — this from an AOPA staff pilot who stands 6 feet 7 inches tall — late-model Archers (those manufactured since 1994, known as Archer IIIs) have a series of differences not unlike their Seminole counterparts that both modernize and organize the cockpit.

Namely, the electrical switches have relocated to sunnier climes on the overhead panel from their previous location in the lower center of the instrument panel. Hank Kumpunem, chief flight instructor at U.S. Flight Academy in Denton, Texas, says, "It appeals to everyone, it seems, and they say, 'It feels like I'm all grown up now, flying something more sophisticated.'" Pilots of vintage Archers recall that the master switch has two "sides," a battery side and an alternator side, and often both are selected at the same time during airplane start-up. However, the newer Archers have separate battery and alternator switches (as do other new Pipers), and this caused one staff pilot to report an error on his part when flying a new Archer after logging many hours in the older versions. "I flew around the pattern in one of the new ones with the alternator off. I noticed it when the GPS navigator started to fail with a flashing light show," says the pilot.

Others on the AOPA staff who have transitioned to the newer Archers note that the start procedure is also somewhat different (there's no key) and perhaps more prone to flooding if the correct technique is not used. During the cold months when engines get cranky, it's tempting to prime a lot and that includes using the primer and "pumping" the throttle. In prior versions of the Archer, the primer is a mechanical plunger with a small throw, only feeding a sip of gas at a time. It takes several shots to prime the engine — and it leads pilots to pump the throttle to compensate, even though this creates the possibility of a fire in the engine compartment with all that fuel. In the Archer IIIs, the primer is electric, and it does the job and then some. If you engage the electric primer and pump the throttle, you'll surely flood the engine. If you pump, do it judiciously and be wary of pumping in addition to priming. Using the primer is the preferred method.

Those new and old 172s

The Aspen Flying Club, based at Centennial Airport southeast of Denver, has both older-model Cessna 172s (such as the M and P models) and newer models (such as the SP). Aside from the modern upholstery, 172s also differ on several important points.

First, to preflight an older 172 meant draining fuel from each wing tank and the fuel selector quick drain, and taking a sample from the fuel strainer drain. For the new models, which debuted in 1997 with the 172R, expect five sumps from each wing, plus two from the bottom of the mid and forward fuselage.

Older 172s are carbureted, while the new ones have fuel-injected engines. From start procedures to emergency procedures you're going to feel your way through some differences if you initially checked out in a 172M or N. The start procedure involves priming the engine using the mixture control, and then engaging the starter with the mixture at full lean, advancing the mixture as the engine fires. Instead of carburetor heat to call upon in moist and cool conditions — and when throttling back the engine — you have alternate air, which is used if ice or snow (or perhaps flying debris) inhibits the main air filter. And there's a fuel pump in the new models to back up the engine-driven pump.

The fuel-injection system may be a first for some pilots, and it also may be their introduction to vapor lock — especially in the summer, according to Aspen flight instructor Adam Sorkin. Also, Sorkin says, "It's really easy to flood an S model. You have to be pretty quick with your hands during engine start."

Because of the altitude at Centennial, Micky Magnolo, manager at Aspen, notes that there's another big difference between the two: horsepower. "Performance at this altitude is better in the SPs," says Magnolo. The SPs have 180-hp engines as opposed to the older 172s, with either 150 or 160 hp, and the 172Rs that have 160 hp.

Then we come to avionics. With the new Bendix/King stacks in the 172Rs and later, as opposed to whatever mishmash you find in an older rental 172, it's a whole new world. The KLN 89B and 94 are "...good GPSs for making the transition into an airplane with a GPS," Sorkin says. And Magnolo adds, "GPS — yep, that changes everything."


E-mail the author at julie.boatman@aopa.org.