Musicians have nightmares about flying with their instruments. Though a mountain dulcimer will almost always fit in overhead storage the instrument is technically too long to be considered carry-on baggage by many airlines.
I rarely have trouble carrying-on a dulcimer. Here are a few things I have learned over the years:
I fly with my dulcimer in a gigbag with a shoulder strap.
A gigbag takes up less room than a hard case and looks smaller and more compact when noticed by flight crews. A shoulder strap lets me carry the dulcimer on my back and leaves my hands free to show my ticket when boarding. Since I am carrying my dulcimer with ease it sometimes goes unnoticed. I rarely have trouble bringing a small backpack and dulcimer on board.
If possible I reserve a seat towards the back of the plane.
Usually the rear seats board earlier and many overhead bins are still empty and available. The flight crews are usually less concerned about this odd-shaped piece of musical luggage taking up space while there is still plenty to go around.
If told my dulcimer will not fit overhead I politely explain that it has always fit in the past.
The flight crew is doing their job. They are people. Be nice to them!
If the flight crew tags my dulcimer to be checked as cargo while boarding a smaller plane I discreetly take the tag off and put it in my pocket .
I have only done this a few times. I was able to carry on my dulcimer with no problem.
There have been a few times when all the overhead compartments were full or an airline employee’s purpose in life has been to keep me from bringing my dulcimer on the plane. In 30 years of flying with a dulcimer I have faced these scenarios 3 or 4 times. In these situations the only option was to have my dulcimer hand-placed in cargo. Theoretically this means it is carefully placed in cargo and carefully removed and given to me as I leave the plane.
When this has happened my dulcimer survived. I survived too but the flight was anything but relaxing!