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Sunday, February 10, 2019

Can Pilots ‘Step on the Gas’ if They’re Behind Schedule?

It’s a familiar scenario for passengers: your flight is delayed by 30 minutes. Then 45 minutes. You risk missing that important meeting. It’ll be touch and go. But then, you board and get airborne. The captain then comes on the PA:
Sorry about the late departure from LaGaurdia, but looks like we’ll have you at the gate in Chicago five minutes earlier than our originally scheduled time. So, sit back, relax and enjoy your flight.”
Wait, what? What happened? Did the pilots step on the gas?
Yes, it turns out they can, and do.

Delta Air Lines had the best on-time performance of any airline in the world in 2018 according to Flight Global, with some 86% of its flights arriving on time. (That’s 6 percentage points better than the US average.) Delta and Lufthansa provided insight into how these mainline carriers use a mix of meteorology, efficiency and pedal-to-the-metal to make up for lost time.

“Our operations teams and crew members have a number of tools in their toolbox to try and make up time for a delayed departure,” a Delta spokesperson said in an email. “These decisions are collectively made with our flight crews as well as the dispatcher or flight superintendent on the ground who evaluate what opportunities we have.”
It’s a similar situation for Lufthansa. “Our pilots are most of all responsible for the safety of the aircraft, the passengers on board and the cargo,” a spokesperson for Lufthansa said in an email. “Under the priority of safety, decisions are made based on economic considerations, comfort and punctuality. Our pilots are authorized to change the speed compared to the original planning under the above mentioned aspects. [It also] depends among other things on fuel reserves, airspace structure, weather conditions. All this must be considered,” she said

Flying Direct

Flights across the US follow certain jet routes. “One of the primary ways we can address a delayed departure is to adjust the flight routing or ask air traffic control for a more direct routing, if one exists,” a spokesperson from Delta said in an email. This means they could potential skip certain waypoints along the route that might add precious minutes.
“Whatever the options, it is a collective decision with our dispatchers and flight crews,” a Lufthansa spokesperson said, noting that the crew and operations review the routings of the previous flights for comparison. “On this basis, the crew can estimate where direct routing makes sense if it is available.”

Mother Nature to the Rescue

The winds aloft at the so-called flight levels — 18,000 feet and above — can be incredibly strong, often more than 100 knots. That provides an incredible tailwind for flights heading east, and headwind for flights heading west, which explains why flights from New York to Los Angeles, for example, can be as much as one hour longer than the opposite trip. If your flight is flying with the benefit of a tailwind, you might be in luck.
The image below shows the flight deck display of an airliner cruising westbound above the US, with a moderate headwind. The red arrow added in the corner of the navigation display shows where the wind speed and direction are indicated. That “260° / 54” means that the wind is coming from almost dead ahead, 260 degrees on the compass, at a speed of 54 knots, or 62 mph. And that wind is exactly what is slowing the plane down. Above the wind indication, you’ll see the airplane’s speed. Relative to the surrounding air (true airspeed, or TAS) the plane is moving at 480 knots; but relative to the ground below (GS, or ground speed) it’s doing just 426 knots, or 490 mph. The difference between those two speeds is equal to the speed of the wind.
Now reverse direction, and the same wind will push the eastbound plane faster — by exactly 54 knots.
Delta said its flight dispatch teams will “work with our meteorology team to see if there are tailwinds (or lighter headwinds) that we can take advantage of, which is typically part of our processes regardless.”

Throttling Up

The airlines aim to deliver. And flying faster is one way to do exactly that. For example, an aircraft can fly at a higher altitude, like they do over the Atlantic, to burn less fuel, have less friction from the thinner air at higher altitude, and often benefit from the aforementioned winds aloft.
Lufthansa crews “may opt to increase the speed of the flight to ensure an on-time arrival,” said the airline spokesperson, but also noted that crews have empirical data such as fuel burn and efficiency at the various phases of the flight. “The pilot in command — the captain — is responsible for flight operations. He [sic] is supported by the ground services. Lufthansa has its own Mission Support department at the traffic control center, which provides the crew on board with current weather data for this purpose.”
The final decision is made by the crew on board.
One thing is certain: it’s always a pleasant surprise to make up for lost time.
Mike Arnot

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