Ask the Captain: Advanced-level plane spotting from readers
Q: I've noticed that only the Boeing 757 has two primary passenger loading doors on the left/port side of the plane, one before and one after first class. Why hasn't this excellent idea caught on in single-aisle aircraft since?
— Sean P., Detroit
A: The location of the door and the dimension of the gate make the B757 a bit unique. The Airbus A321 will occasionally use the second left-hand door (known as L2) for boarding.
Only the longer fuselages have room for the loading bridge in front of the wing.
I agree with you that it improves the ease of boarding.
Q: Can you tell the difference between Tu-204 and Airbus A-320?
— Pramuditha, Russia
A: Yes, there are several differences. The A320 has only two tires on each main gear, where the Tu-204 has four. The nose is different, too.
Q: What is that little device on the MD-80's nose gear?
— Patrick, Los Angeles
A: I suspect you are asking about the spray deflector that is attached to the nose gear just aft of the tires.
The spray deflector reduces the water that is ingested by the engines during takeoff and landing.
Q: Why do Boeing 777 aircraft not utilize winglets for improved efficiency?
— Bruce Casey, Fort Lauderdale
A: The Boeing 777, like the Boeing 767-400 and 747-800, have raked wing tips that provide nearly the same benefits as winglets. Winglets are not the only way to manage the wingtip vortices and extract extra performance while improving fuel efficiency.
Q: When an MD-80 engages reverse thrust, two reverse deflectors come out and cover the exhaust of the engine. But when a 777 engages its reverse thrust, a cover slides back, nothing protrudes from the side of the engine, and air is forced forward from the side of the engine to help slow the aircraft. Is that reverse thrust coming from the hot exhaust of the engine, or just from the turbofans? Is there still exhaust coming from the back of the engine while reverse thrust is engaged on a 777?
— Michael Dunn, Dallas
A: You are correct. The MD-80 series thrust reversers are close together, deflecting the fan and exhaust air forward. Most modern jet engines (the MD-80 engine, the JT-8D, was designed in the early 1960s) deflect only the fan air to reduce noise.
On a 777, the sleeve that you reference moving aft sends deflector doors into the fan duct, causing fan air to be deflected forward.
Because the fan produces so much of the total thrust of modern jet engines, reverse thrust is very effective using only fan air.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.