It already has happened.
http://www.citizen-times.com/apps/pbcs.dll/article?AID=200880327021
I definitely do see this as a AD potential. Duty and off-duty holsters are designed specifically to cover the entire trigger as to avoid objects from getting in between the trigger. Apparently 'da boneheads' at TSA thought by MODIFYING a typical off-duty type holster as such by poking a hole in it for a pad lock would make the weapon safer.
Bear in mind; TSA officials (management) doesn't really mean they are fully trained at the subject at hand nor may they be subject matter expert. The tons of Air Marshall's they hire right after 9/11 ( I even threw in an app) a majority being from BP Agents (and many came back to the BP) get really good FA training. I also trained with them and their FA instructors take our (BP) FITP, Firearms Instructor's Training Program. I also got a change to get some of their training and at the same time they were putting many pilots through their weeklong FA training at Artesia (In the video above I think that's Artesia).
However a TSA management may have come from a different background such as USDA, maybe Postal Inspector, who knows? But they do have a cadre of management that really don't get much field time or in the course of their career may draw down but a few times.
That holster shown in the video does not come like that. So obviously someone at TSA devised a policy requiring such security device that defeats the purpose to have a trigger completely covered. It's bad enough hearing how people leave their finger in the trigger as they re holster, but now the pilots are made to place a bar in a hole like that.
As a habit I continuously check my gun and snap. Yes, seat belts, shirts, elbows are the usual culprits. I used to use a Safariland level III double snap model with my Beretta. Now I have the issued level II bail retention. Even those become unsnapped/bail unhooked. I've found both snaps undone on a number of occasions. I can also see the gun working its way out if one has to put on and take off.
I'm not positively sure wether the pilots who get trained keep on to that gun or if it is left locked in the plane. I think the pilot brings it on board because not all of them want to carry. Just as with LEO and MIL, many don't have have formal or any previous training or experience. They only get one week and who knows about needing follow up quals. Few may be gun nuts and will have more experience and savvy. Although it's usually the 'experts' that have a ND/AD.
If that is TSA's policy, yes it is an accident waiting to happen.... again.