Captain Mike Bowers is Chief Pilot at our Newark Liberty International Airport (EWR) hub. This new United Hub series is based on our column in Hemispheres magazine, in which Mike answers questions from our customers. Every month, we’ll feature a few new questions and answers.
Q: When flying at 35,000 feet, what is the maximum distance, in miles, that we can see on a clear day? What about at 40,000 feet? At 30,000?
A: Many factors affect the visible distance to the horizon, including the geometry of the curvature of the earth and the effects of atmospheric refraction. To simplify the answer, if we consider only the geometry, the formula for distance (miles) is 1.22 multiplied by the square root of the height (feet) of the aircraft. I won't make you do the math.
At 10,000 feet you can see 122 miles, at 30,000 feet you can see 211 miles, and at 40,000 feet you can see 244 miles. Of course, if you look "above" the horizon, you can see the sun at 93,000,000 miles and at night, even further, to the stars.
Q: Let’s say that a flight is delayed and departs one hour after its scheduled departure time. Can the pilot increase the speed of the plane to make up for the lost time and arrive at its destination a little faster?
A: We measure our cruise speed in "Mach." Mach 1 is the speed of sound. Depending on aircraft type, a typical cruise speed would be .78 Mach or slightly above three-quarters the speed of sound. The fastest speed that a typical airliner can fly is about .85 Mach, so we can and do increase our speed slightly to make up for late departures. But that increase of .07 Mach is only about 42 miles per hour. On a six-hour flight, that would equal approximately 252 miles, which is just about 30 minutes of flying time.
By flying at maximum speed we can decrease the flying time by about five minutes per hour. The reason we don't normally fly at maximum speed is because, just like with your car, the faster we go, the more fuel we consume. Higher fuel consumption can drive up the price of tickets and create more pollution.
Q: I live in Florida and often take the last flight of the day back home. I have noticed that last-flight-of-the-day flights last significantly longer than those at any other times – often 30 to 40 percent longer than a morning or afternoon flight with the same itinerary. I have been told that it's just my impression, but the watch doesn't lie. Then I started noticing that the air speed, shown on the inflight travel map, is significantly lower on these final flights of the day.
My question is: Is it company policy to go slower and conserve fuel on flights where it is known that there are no more connections that day? By overwhelming majority, the passengers are returning to their homes, so is the airline assuming it is okay to take longer to get them home?
A: We do not alter our speed on the last flight of the night. Some aircraft cruise slower than others and perhaps those later flights operate with slower planes. But that would only result in a few minutes difference, not the 30 to 40 percent you mention.
More likely, if you are returning home to Florida by flying south, you will be flying into a headwind because the jet stream tends to travel toward the northeast. That would increase the flight time. Also, earlier flights going north gain the advantage of that wind, which would result in a tailwind pushing them faster.
Q: Why do some runways crisscross each other? When a flight lands or takes off, are both runways reserved?
A: Because we always want to take off and land into the wind, airports are designed to align their runways with the prevailing winds. Wind patterns can change with varying weather conditions, so most airports have additional runways aligned with different potential wind directions. Unless the airport has a large amount of area to use, the runways normally cross each other.
When wind conditions allow for the use of more than one crossing runway, the airport can operate with multiple runways available. However, the air traffic control tower coordinates the flow of traffic to ensure that no crossing runways are used simultaneously.
Do you have a question for our pilot? Send these to firstname.lastname@example.org. For more of Mike’s answers to passengers’ questions, take a look at Hemispheres magazine during your next flight with us.