Originally Posted by
Nightflyer
When I was on the 777, it was maintenance. They do it so they don't have to clean the ovens. The bottom shelf covered in foil keeps food from dripping on the bottom of the oven.
Personally, I used to remove the foil every time I saw it.
Like the OP said, it's a convection oven. It does not work if the air cannot circulate. The holes exist to facilitate the air circulation.
I use a sharpened credit card, also useful for cutting LA catering tape, to make an X in the foil over the holes then fold the foil back. If my credit card needs sharpening I use my finger and poke the foil. I have also found that second generation Tempe Mission Palms pen will do the trick in a pinch.