The Floor is Making Noises!!

There are times when we are at work and we have to make decisions to ground a plane or not ground a plane. We never take these decisions lightly and of course we know that the impact to passengers and schedulers are going to be huge. There are times, however, that require us to ground a plane when we suspect there is no real problem. This is exactly what happened to us last week.

One of the guys got a call for a chat, lets call him-Baby Boy. So Baby Boy goes out and gets into this "discussion" with the on coming Captain and an off going Flight Attendant. The FA says that when she walks down the center aisle by the overwing exit the floor panel makes a popping sound. The captain that is supposed to take this flight out is well known to us mechanics and is a nervous wreck, since he is famous for grounding planes because of the floor placard that shows the pilot seat position I'll call him Capt. Placard.

By the time Baby Boy gets up to the plane the FA has Capt. Placard convinced that there is some structural damage to the floor of this plane. I should mention that the plane is a 737-700. After trying to calm down the captain Baby Boy comes back into the office looking for advice. Since I have worked overhaul I knew that the popping sound the floor panels make are because of foam tape which is put on the panels where they rest on the floor beams. After some time the tape wears through in spots leaving the sticky part of the tape on the panel. When a person steps on it the sticky part makes contact with the floor beam, when that person lifts his/her foot the adhesive lets go of the floor beam and the panel makes a popping sound.

Baby Boy went back to the plane to explain this to Capt. Placard but by now he was sure the floor was about to give way. He stepped on either side of the aisle by where the passengers at seats 12C and 12D would have their feet and sure enough the floor flexed and there was no way to talk him off the ledge at that point.
 

All of us agreed that baby Boy should just ground it and get Capt. Placard a different aircraft. Not being a shy person Baby Boy let Capt. Placard and the FA know that this was not cool and basically a waste of time.

I went out to Tango (where we park our planes away from the terminal) to help Baby Boy pull up the floor panel in question. Since this was an "evolve" aircraft we pulled up the carpet squares and went to work on the floor panel fasteners. Some of them were stripped (of course) so we drilled out about four of the about 50 screws and pulled the panel back. Normally to get that panel up you would have to take off about six or seven rows of seats. We tried something new and were able to pull the panel up slightly and then down the aisle by sliding it along the aisle and under the seats. Guess what we found-NOTHING.

Floor panel up

The foam under the panel was worn which Baby Boy replaced. The flexing of that particular panel happens because of its position. The panel is located right over the wing box area and as such there are few lateral supports to attach it to the aircraft structure. Most panels have the long floor beams running the length of the plane and several intercostals (non structural beams running across the cabin from floor beam to floor beam. The wing box area is built in such a way that those intercostals are not installed there, as such the floor panel itself has to span a wider area and it flexes more than others do. Also this is a 700 aircraft, when they built the thing they tried to save as much weight as possible and left out as many of those non-structural intercostals as possible.

Waiting out on the wing for parts.

All in all it was a wasted effort but I wanted to show Baby Boy and the other guys that the popping sound it nothing to worry about and can be explained away. It was a beautiful day out there and we had all the doors and overwing exits open to enjoy it. We had the plane back in service in a couple of hours and learned something while doing it.