Airplane (Air Pain?) Travel

Paul Greenwaltby Paul Greenwalt, EIT

Recently, my wife and I decided to finally visit a college friend of mine in her hometown of Sitka, Alaska. We made our way to the airport, breezed through security, and headed to our departure gate.

We were flying with Alaska Air on “standby” and had to wait until all “paying” customers were checked in and assigned seats before the gate agents could release the remaining seats to standby passengers. Luckily there was plenty of room on the flight and we were placed in row 25 of our Boeing 737-400 jet.

This aircraft seats 144 passengers, 12 of which are first class. It is just shy of 120 feet in length and has a 94 foot wingspan! Its cruising speed is 500 mph. It is operated by two pilots and three flight attendants. This twin-engine jet has a range of 2,400 miles at a maximum gross weight of 138,000lbs (it weighs only 35,000lbs empty). The engines each deliver 22,000 pound-force of thrust. (Read here for more fun facts about the Boeing 737-400!).

Ready for Take-Off…Not!

Back to my story. As we got settled in to our seats the flight crew announced that they were not our scheduled crew. They were just filling while we waited for our actual crew to land and make their way across the airport to take over. Okay, so that’s not the end of the world. Just a few minutes and we’ll be on our way…or so we thought.

“Hello, this is you Captain speaking. While we wait for the flight crew to arrive, maintenance has noted a bad shock in the landing gear and are going to repair it. It could take up to 30 minutes, so sit tight and we’ll be off the ground as soon as they finish.”

Five minutes later…

“Well, folks. It looks like maintenance is going to need more time, so we are going to deplane and head to a new gate where we have another plane ready for takeoff.” So we all grab our stuff and head to the new gate, re-board, and wait for the luggage personnel to move our bags from one aircraft to the other. We made it to our destination without any other problems, but what might have been? The landing gear fails at our minimum air speed of 155mph? Hmm…not ideal. Thanks to the diligence of aircraft maintenance personnel for saving our lives!

There and Back Again

Our non-stop flight from Sitka to Seattle had a “stop” in Ketchikan. I’ll say that again…okay, you get the point. When we landed to drop off some passengers and pick up a few others, the pilot announced that the outside air temperature probe had failed on our short flight over from Sitka. It would need to be replaced. The Ketchikan airport didn’t have the replacement part on hand so it was expedited over from another airport on an inbound flight to Ketchikan. Once it arrived, it was installed and tested.

Testing Testing…

Great! We should be re-boarding and off to Seattle, right? No. The Ketchikan airport is so small that they did not have a testing device (an ohmmeter) that was FAA-approved, calibrated, and accurate to within one hundredth of an ohm. Once the airport maintenance crew discovered this, they did the same thing as with the air temperature sensor – expedited one to Ketchikan on a flight coming in from…Seattle. Ugh!

3 hours later…

Before the testing instrument actually arrived, the airline had everyone re-board the plane so we’d be ready to go immediately after testing was complete. Our flight crew was approaching their maximum allowable 16-hours on shift (including a 2 hour extension on their scheduled shift)! As we all got seated back on the plane, flight from Seattle with our ohmmeter pulled in to the gate. Testing commences, the new probe pass, and we are off!

A Job Well Done

While some passengers were put out that they missed their connections and that they had to wait in the airport for nearly 7 hours, I commend the aircraft maintenance staff, the flight crew, and the airline for their efforts to keep us safe! I learned something new in the wake of this incident. It turns out that pilots don’t just smile mischievously when they get to read that the plane is flying through -65℉ ambient air at 500mph, 35,000 feet above the surface of Earth. It is much more than that! The air is vastly different at this altitude, creating a number of unique considerations that pilots and planes must address.

Depending on the temperature, humidity, wind speed, and other weather phenomena, a pilot may decide to alter the flight course to speed up the flight time, reduce turbulence, or avoid ice crystals or lightning.

This temperature probe is an essential sensor for the Engine Control System. Jet engines require inlet air temperature readings to calculate performance and optimize fuel-to-air ratios and compression ratio. Without this, the plane may not optimize fuel consumption and who knows how far you’ll get! True airspeed computation is another piece of vital information that relies on the outside air temperature. True airspeed is calculated using outside air temperature, the specific heat ratio of air, the gas constant, and the Mach number. Suffice it to say that without this device, long distance travel would be lower and slower! Props to my homies in aircraft maintenance!

 

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