The first thing you are going to need is a letter from a doctor certifying that your father is okay to fly. At 87 and a nursing home patient, the airline is going to require such a letter before issuing him a ticket. You will also need to make sure when booking his ticket that the airline understands he is a wheelchair passenger who requires assistance, even if he can still walk. Depending on the airports you transit through, the distance between gates can be quite far (and fatiguing even for us younger folks).

When packing for the flight, make sure all his medications and his medical records are in his carryon bag and not in his checked luggage. You can't take bottled water through security, but you can usually buy some after clearing security. Do so. He will need the water for his medications, and to prevent dehydration while in flight. Snack foods he likes such as fruit or crackers and cheese are also advisable since meals will be irregular (and on planes sometimes inedible) on the day of travel.

Try to get to the airport well ahead of normal check-in time. It's annoying to have to sit and wait, but with airline travel these days, if something can go wrong it probably will, so it is good to have extra time to iron out any glitches that might occur.

A change of clothing in his carryon bag might also be advisable. His clothing should be loose fitting, comfortable, and easy to change in the event of an accident. As DeafFlyer says, it is easier to tend to bathroom needs in an airport than on a plane. Most airports now have what are euphemistically called "family" toilet areas where a passenger who needs assistance can be accompanied by a family member of the opposite sex.

That's all I can think of for the moment. Good luck with your trip. As you can probably tell, "been there, done that."