Plane Answers: Water vapor in a jet’s A/C, flashing landing lights and a fuel question.

Welcome to Gadling’s feature, Plane Answers, where our resident airline pilot, Kent Wien, answers your questions about everything from takeoff to touchdown and beyond. Have a question of your own? Ask away!

Zach asks,

Hi Kent,

My family and I recently flew from Cancun to Philadelphia. On the ground in Cancun, I noticed some sort of condensation coming out of the air conditioning ducts. To tell you the truth, it looked more like smoke than water vapor. The flight attendants didn’t seem to mind, and once we took off, the condensation dissipated. I’m a student pilot and a fairly frequent flyer, but I have never seen anything like it before. What was happening?

You’re on the right track, Zach. We often see condensation from the air conditioning ‘packs’ on airliners in hot cities with high humidity. On the 757 we often get so much moisture that we’ll see frozen ice pellets coming from the air vents. Enough ice can build up in the packs that the airflow drops off to almost nothing until we run the temperature to a warm setting for 30 seconds or so to melt this ice.

In flight, it doesn’t seem to be an issue at all, probably due to the drier air.

Irwin asks:

Recently, while waiting for a flight to arrive at West Palm Beach, FL, I watched another flight from a distance of several miles while they were on approach. As it got closer to the airport, I noticed his headlights were turning on & off, constantly, equal time on & off. There were no clouds and no obstructions of any kind. What was the pilot doing or signaling?
You more than likely saw a Southwest jet. They’ve equipped many, if not all their 737s with flashing landing lights that are supposed to make the aircraft easier to see inflight. Some corporate aircraft have had this feature for years and it may be coming to more airlines in the future.

Louise asks:

Where is jet fuel carried on passenger jets? …in the wings, the belly, below the luggage compartment? …or somewhere else? (We are trying to figure out what made that US Air plane FLOAT, even though the passenger compartment flooded… then we got curious… where IS the fuel stored/carried?!)

Thank you!

Most airliners store the fuel exclusively in the wings. Occasionally companies have offered long range tanks that take a small portion of the fuselage near the forward part of the wings for extra fuel at the expense of baggage area, but this is rather rare today.

The US Airways flight likely had only half of the maximum capacity of fuel on board. We’ve been told that an airliner is capable of several minutes of flotation and US Airways 1549 demonstrated that even with a torn lower fuselage, there was enough time to evacuate the aircraft.

The entire industry learned a great deal from that ditching.

Do you have a question about something related to the pointy end of an airplane? Ask Kent and maybe he’ll use it for next Monday’s Plane Answers. Check out his other blog, Cockpit Chronicles and travel along with him at work.