Archive for ask an airline pilot

Ask an Airline Pilot

Posted in air travel, airline pilot blog with tags , , , , , on August 13, 2012 by Chris Manno

Have questions you want to ask an airline pilot but don’t have one handy? Or you notice that they’re busy with pre-flight duties (thanks for noticing and for not interfering) so you don’t say anything?

Here are the questions I get asked most often, with the best answers I can come up with:

1. Do personal electronic devices interfere with aircraft systems?

Answer: Here’s what you have remember about aircraft systems and electronic devices. First, many handheld or personal devices create an electronic signal, particularly if they have a cord of some type. Aircraft systems are constantly seeking out specific electronic signals from everything from Global Positioning Satellites to ground-based antennae for communications and navigation.

Further, even within the aircraft, there are electronics creating and transmitting electronic signals between systems for both navigation and control of other aircraft systems–including flight controls. It’s important that only the required signals are received by specific on-board systems and yes, extraneous electronic impulses can interfere with those required for control of various navigation and control functions.

Most have backups with non-electronic signals. For example, on the 737-800, the engines are controlled by an advanced solid-state dual system we call EECs. For every throttle movement, the EEC computers are sending impulses to the fuel control based on hundreds of minute electronic inputs from computers, sensors, instrumentation, and pre-programmed performance parameters. Worst case, though, if there is an interference problem or a failure, the system reverts to a “dumb” mode, simply using the old direct throttle and hydro-mechanical linkage. So in this case, any electronic interference is not a major problem–just an inefficiency.

Ditto in the approach mode: the aircraft navigation systems are receiving and displaying course and altitude data from ground-based antennae. If there’s a conflict or interference, we simply don’t use the data. That only changes the minimum descent altitude which again, is an efficiency issue: might have to divert if we can’t descend below the weather.

A final and more important consideration is in play though, when it comes to personal handheld devices during critical phases of flight. That is, the personal attention of the passengers–which needs to be directed to the crew. Not watching a video, or typing a text message, or listening to music. In critical phases of flight, passengers need to focus on and attend to the instructions of the crew.

2. How fast are we going on take-off and landing?

Answer: Well, it varies based on aircraft weight and flap configuration, but you can pretty much figure in a large jetliner that both the take-off and touchdown speed will be between 130 and 155 miles per hour (of course we use nautical miles per hour for our calculations). The jet will normally fly about ten knots shy of the computed take-off speed, but that is a minimum that doesn’t ensure maneuvering speed margins.

Speeds on takeoff and landing are always a spectrum of choices for the pilots. On take-off, we consider the climb gradient required due to obstacles or terrain ahead. More flaps offers a higher climb gradient and a lower take-off speed. A lower flap setting requires more runway for take-off but most likely can allow for a reduced power setting, important points for engine life and even noise considerations.

The short runway at Santa Ana's John Wayne Airport is always a performance challenge for both take-off and landing.

On landing, the higher flap setting allows for a slower approach speed, which is key when landing on a short runway. An interesting point you may not realize is that by design, the profile speeds for the stretched aircraft like the 737, 757 and 777 are artificially boosted to keep the nose position relatively low through both the take-off and landing rotations. That’s because the geometry of the stretched fuselage leaves a critically small margin between the tail and the runway on both maneuvers: in the 757, you have about 18 inches between the tailcone and the runway on take-off rotation and landing flare–not really much clearance. The higher approach speeds keep the nose lower.

Of course, upon landing on a short field like Santa Ana or even Washington Reagan or LaGuardia, the last thing you want is excess speed to absorb in stopping. No worries though: Boeing has given us the toughest landing gear and brakes in the air today.

3. Are most landings done by automation?

Answer: No. In fact, very few are, for a couple of good reasons. First, the ground based antenna must be kept free of any obstructions, and that specification and guarantee is only provided in very low visibility, which in itself is unusual. I mean that literally too: the airport physically ensures that no ground traffic of any kind–airport vehicles or aircraft–taxies by the antenna while an aircraft  is using the signal for landing guidance.

If the antenna isn’t specifically certified as free from any interference, the landing will not be automatic. Also, a special crew certification is required for autoland, and not all aircraft are equipped to do it: MD-80s, 757s, 767s and 777s  can all autoland if the correct conditions exist. But the 737-800 I fly does not have the capability to autoland. Rather, we have the cosmic Heads Up Display that allows me, the captain, to land with no ceiling and only 300 feet of forward visibility:

I can “see” the runway through whatever weather shrouds the actual runway–because the GPS system synthesizes a runway which exactly overlays the actual runway and I’m watching it all the way down. So at least in the 737-800’s I fly, you’ll never have an autoland and will always have a hand-flown approach and landing. And even when I flew the autoland-capable MD-80, I’d perform maybe one or two actual autolands per year. So the answer, generally speaking, is no, aircraft aren’t normally landed “automatically.”

Whatever the visibility, the Boeing-737-800 at my airline is landed by hand.

The last question that goes with the group of “most asked” I won’t even answer, and I usually don’t when inevitably, someone has to ask: “Where is the   nearest bathroom?” The answer is, “I’ve answered the important questions above–I’ll leave this one up to you.”

%d bloggers like this: