The company is negligent if it doesn't oversee their subcontractors and hold them accountable for their work. Likely criminal.
That is not 100% correct.
If say a company is subcontracting out the "snow clearing" work. The company has the responsibility to make sure that is it done. If it is not done, the company could fire the contractor or tell them to follow the contract. However, if someone slip, the company is negligence. The company then could sue the contractor for damage of void of contract to recover the damage of the negligence claim. The whole deal would not be criminal at all.
On the same line, if the airlines have utilized reasonable line checks, with good record keeping and SOPs they follow, the airline would not necessarily be liable.
The claim one would probably use under the plane dropping situation would be "Res Ipsa Loquitur" (the thing speaks for itself, which includes 3 elements...
- the event does not normally occur without negligence
- exclusive control by defendant
- no provocation / contribution by plaintiff.
The third is relatively easy to prove. The issue is the first two. Does the plane normal drop from the sky without negligence? On one hand, planes don't normally drop from the sky. On the other hand, planes dropping from the sky doesn't neccesarily mean negligence. Is the event controlled by the defendant exclusively? Not really. That would depend on the investigation report of the accident, which could at times be inconclusive. If the plaintiff can't prove all 3, then they would have to fall back to proving the duty, breach, injury, and causation. Duty and injury are easy. Causation again depends on the investigation. Breach is the tricky one. Does outsourcing mean breach of duty? If the airlines perform checks, but somehow everything checked out right... is that a breach? That is a debatable issue. (Bare in mind no airlines operating in US would send planes in the air with pax if there are any doubts about the safety, yet accidents still occur.)
Strict liability doesn't apply here because strict liability refers ultrahazardous activities that could outlawed because of the danger it creates. I don't think we could say flying on a commercial aircraft is "ultrahazardous".
The whole negligence law is to encourage people to act reasonably. It is not to encourage all companies to do everything under one roof without any outsourcing. If you skip directly from outsource = save cost = lower quality = disaster, that is a bit too biased.
That being said, the airline is not always liable. It could be the contractor, the manufacturer, or whoever else that is involved. Fining airlines prematurely is not a reasonable act.