I was waiting in the Seattle airport the other day for my flight home. A group next to me was too loud to ignore. When they first saw the airplanes parked along the gerbil tubes, one person said “I didn’t sign up for a propeller airplane.”

I bit my tongue, though I was in a feisty enough mood to embarrass stupid comments. I was in uniform and thought it best to behave myself. She had signed up for a ‘propeller airplane’. When her ticket was purchased, I have a sneaky suspicion price was the only concern. I doubt the ticket buyer looked at plane type.

The propeller versus jet distinction is odd. Passengers, and all too frequently new pilots, have a misguided perception of the difference between the two.

As I have climbed up the pilot career I have flown airplanes with two power plant types. Piston engines operate in the same manner as car engines. There is a piston moving in a cylinder. After the ignition cycle, the piston pushes the rotation of the crankshaft. In a car the crankshaft is attached to a drive train of some sort transferring power to the wheels. In an airplane the crankshaft is attached to the propeller; it is usually a direct connection.

Gas turbine engines are the other type of engine found in civilian airplanes. Gas turbine engines are laid out differently as they pull the power from the exhaust cycle rather than the combustion cycle. The gas turbine started its history powering airplanes in a pure form. That is, the core engine supplied the power. As the engine has evolved, the way the power is pulled from it has changed.

The turbofan engine takes the core and attaches fan blades to the front. The fan blades are pretty much large versions of the compressor blades. They are enclosed in the engine shroud, making it difficult to see the ‘jet’ engine on your airliner has shrouded, non-variable, smaller diameter propellers hidden from view. Much of the air the fan blades expel bypasses the engine core and goes straight into creating thrust for airplane propulsion.

The turboprop engine takes the core and attaches it to a gear box, which then turns propellers. Gas turbine cores rotate far too fast for propellers to aerodynamically work. So the gear box has to slow the rotation.

In the United States, the only scheduled air carrier I am aware using piston powered airplanes is Cape Air. Outside of that, all other propeller airplanes you see in airline service are using turbine engines; the same as the ‘jet’ you might see sitting next to them.

Comfort

I occasionally commute on another airline that uses a different type of turboprop. The airline is wonderful to me, and I appreciate that a great deal. But their turboprop, the EMB-120 Brasilia, is uncomfortable. At my measly 6 ft tall my knees are buried in the seat in front of me, and I have to hunch walking down the aisle. The interior is loud and vibrates.

I can see where passengers conceptions of turboprops comes from. The older airplanes are lacking. The propellers vibrate the airplane more than jet engines. The propellers bombard the fuselage with sound waves. Turboprops are typically smaller and very cramped. Many types are significantly slower than jets so they take longer to get places. And they don’t fly as high as jets, so turboprops are often stuck slugging around in the clouds and bumps.

Passengers are often surprised by the Q400 I fly. It has an active noise and vibration suppression system (ANVS). When the ANVS works, the interior noise and vibration is similar to a jet. Seat room is still cramped, but it is on par with large-jet economy seats.

From my crazy perspective of sitting in the back while commuting, the Q400 has a more comfortable cabin than the Bombardier regional jets. The Bombardier regional jets have the same fuselage diameter as the Q400. However, the floor in the jets is higher. So the Q400 has a taller cabin and is wider at shoulder height. The Q400 seats are not very comfortable, but they are tolerable. The Bombardier regional jet seats were purposely made to cause lower back and butt pain; and I am not the only person to whine about this.

I do not have any experience with the other two turboprop airliners, the ATR42 and ATR72, in production. I would imagine the manufacturer goes to the same lengths to attract passengers to the comforts of modern turboprops.

Safety

Passengers have valid concerns with turboprop comfort. However, the misconception that turboprops are inherently unsafe is baseless. Turboprops are designed and tested to the same safety standards as their jet counterparts. They have the same system reliability and redundancies. Turboprops are technologically equal to jets. And they use the same ultra-reliable gas turbine core.

Turboprop engines are a little weaker in one regard. The gear box is a complex hunk of fast moving parts that turbofans don’t have to worry about. Gearboxes do sometimes fail. I remember in my previous job listening to a co-worker on company frequency return to an airport after the gearbox failed on one of his engines.

I read a newspaper article soon after starting my airline job that was crying about a new local airline starting service with ‘dangerous’ turboprops. The article cited the lack of drop-down oxygen masks. Drop-down masks are only required if an airplane is certified to fly above 25,000 ft. They are not necessary below 25,000 ft as the airplane can descend to a safe altitude in plenty of time to keep the passengers out of danger.

Aerodynamics

Most turboprops do not have swept wings. Swept wings produce more lift for a given wing size. But more importantly, they allow an airplane to fly at a higher airspeed before the wing airflow exceeds the speed of sound. Wing airflow exceeding the speed of sound is bad unless an airplane is specifically designed for super sonic flight. If an airplane isn’t expected to approach the speed of sound, then swept wings are avoided as they add structural complexity and cost.

Turboprops aren’t designed to approach the speed of sound because of the limitation of the propellers. If the propellers exceed the speed of sound, that portion of the blade going too fast becomes a speed break rather than making useable power. The airplane forward momentum is added to the rotation speed. This is why turboprops can’t move through the air as fast.

The Q400 is a fast turboprop. Predecessor turboprops cruised around 270 knots. Jet airliners typically cruise 400 to 450 knots. The Q400 cruises at 360 knots. The newer versions of the ATRs that is currently in the works are supposed to have faster cruise speeds too. On the shorter legs the Q400 flies, the jet speed difference does not make much of a time advantage.

Economics

Each turbine propulsion type has specific advantages and efficiencies. Turboprops are limited to slower speeds, but they burn significantly less fuel on shorter flight segments.

My employer touts the fact that the Q400 burns 30 percent less fuel than similar size regional jets. That is a whole lot less, especially considering we carry more passengers than the jets they are comparing.

I had the opportunity to look through a cost chart for specific airplane types. It measured the cost based on how much it took to move one seat one mile with each airplane (a fair way of comparing apples to oranges). Most regional airplanes are expensive to operate per available seat mile compared to newer mainline airliners. The smaller planes are still used because the cost per available seat mile is calculated using all the seats on the airplane, regardless of how many are actually filled. A next generation 737 is cheaper per available seat mile than a regional jet. But it costs more to operate the 737. If there are only enough passengers to fill a regional jet it is better to fill the smaller airplane.

This is where the Q400 and other large turboprops shine. Their cost per available seat mile is equivalent to the next generation 737s. Airlines can put a smaller airplane into a market to match demand without taking a hit to the bottom line.

The economics of turboprops versus regional jets is complicated by a concept called cost index flying. Cost index flying takes all factors of operating an airplane such as fuel, maintenance, and crew costs. It then figures out the best airplane for a route and goes even further and plans flight profiles to make the flight as cheap as possible. With cost index flying, regional jets can actually be cheaper on longer legs. Turboprops do burn less fuel. But, if they take substantially longer to fly a leg other costs will increase such as maintenance and crew costs.

The Future

The future for propulsion choices is murky. Pratt & Whitney is working on a geared turbofan. The geared turbofan takes the large bypass advantages of the turboprop and combines it with the speed abilities of a turbofan. The geared turbofan is said to burn considerably less fuel than current generation turbofans and is quieter.

General Electric is working on the ultra high bypass turbofan. This engine uses open rotor technology where the fan blades are not contained in a shroud or duct. The un-ducted fan promises considerable fuel savings too. However, it has been visited before but was abandoned due to noise issues. Manufacturers are currently working on the noise problem.

Each of the new engine technologies can very well erase some of turboprop’s fuel savings. The geared turbofan is already slated to power new airliners currently in development.

ATR is working on new variants of the ATR42 and ATR72. The –600 variants will feature a more advanced flight deck with additional capabilities. The –600 variants will have improved performance and increased passenger comfort.

Bombardier is studying a stretched variant of the Q400, and that they will likely go ahead with the new design. They have not yet finalized configuration or passenger capacity but said it will seat 90 to 100 passengers.

Turboprops Impact on Pilot Career

When pilot employers require prior turbine experience they usually don’t care about the type of turbine. That is, turboprop experience is considered equal to regional jet experience. These employers are more interested in pilots having experience with complicated airplanes operated in complicated environments.

There are a few exceptions. A high profile employer I am aware of, Emirates Airlines, requires the turbine time to be in a ‘jet’. I am not aware of any United States employers specifically requiring ‘jet’ time.