On February 20, 2021, a United Airlines Boeing 777-200 departed Denver, Colorado, and was bound for Honolulu, Hawaii. Shortly after takeoff, the aircraft suffered a catastrophic engine failure, which caused a large amount of debris to fall into the suburbs of Denver. The aircraft was forced to make an emergency landing at Denver International Airport. While no one was injured (on the aircraft or on the ground), alarming images have surfaced of debris on the ground, including one of a large engine cowling in a front yard.

The same day, a Longtail Aviation Boeing 747-400 cargo plane departed Maastricht, Netherlands and also suffered an engine failure that caused debris from the engine to fall below into the town of Meerssen. The debris injured two people and damaged several homes and vehicles.

While instances of debris falling from an aircraft are extremely rare, these instances can raise interesting legal questions as to liability. In situations such as the ones detailed above, it is at least apparent where the debris came from. In some rare cases, ice can accumulate on the aircraft or its ventilation systems, and can eventually become dislodged and fall to the ground. In these cases, especially in the close vicinity of an airport, it may be difficult to pinpoint where the debris originated. In these cases, investigative bodies such as the Canadian Transportation Safety Board will liaise with NAV Canada in an attempt to determine the source of the debris. Once the source of the debris is identified, the question sometimes becomes – who is at fault, and on what standard?

In Canada, there are no specific rules governing the liability of air carriers for ground damage. As a result, the law that applies is the common law of the province in which the damage occurred. However, what standard a Canadian court might apply to a defendant is not necessarily clear.

In the early days of aviation, an aircraft operator was strictly liable for damage caused by aircraft, meaning that the plaintiff did not need to prove that the defendant was negligent in order to recover. A New York decision from 1822, Guille v Swan, involved a hot-air balloon that inadvertently landed in a vegetable garden in New York City. A crowd of onlookers trampled the garden in an attempt to rescue the balloonist. While the balloonist had not been negligent, he was found liable for the loss of the vegetables. This was because he was partaking in an "ultra-hazardous" activity, for which strict liability was appropriate.

Today, commercial aviation has reached a level of safety such that it is not an ultra-hazardous or abnormally dangerous activity, which suggests that a person would likely need to prove negligence for damage or injury caused to those on the surface to be compensable. However, some scholars have contended that strict liability should continue to apply to aircraft operators for injury and damage caused to those on the surface. This is based on the principle of non-reciprocal risk (the risk to the victim outweighs and differs from the risk of the defendant).

While courts in Canada have yet to consider this issue, courts in the United States are shying away from the imposition of strict liability. For instance, in Crosby v Cox Aircraft Co. of Washington, 109 Wash.2d 581 (1987), a property owner brought an action against an owner and operator of an aircraft for ground damage caused by a crash landing. The trial judge imposed strict liability on the owner and operator of the aircraft for damage caused to the property. The Supreme Court of Washington overturned this decision, narrowly deciding in a 5-4 judgement that owners and operators of flying aircraft are liable for ground damage caused by such aircraft only upon proof of negligence. The Court left open the possibility for the doctrine of res ipsa loquitur to apply, which is essentially the inference of negligence in the absence of direct evidence. It is worth noting that the doctrine of res ipsa loquitur was specifically rejected by the Supreme Court of Canada in Fontaine v. British Columbia (Official Administrator), [1998] 1 S.C.R. 42.

The International Civil Aviation Organization (ICAO) attempted to address this issue in the early 2000s when it introduced draft treaties that would impose strict liability on-air operators for surface damage (subject to limits of liability), and similar to the Montreal Convention. The draft conventions have failed to gain enough ratifications by member states to enter into force.

It would be interesting to see how a Canadian court would treat falling debris, and what standard an air carrier would be held to for damage caused by debris. It is likely that the appropriate standard is negligence, which recognizes that an instance of falling debris may be caused by negligence in manufacture, design, or maintenance of an aircraft or part of an aircraft, or by the air carrier owner or operator directly. While this standard of proof may impose an additional burden on those who suffer the loss, applying negligence as opposed to strict liability ensures that at-fault parties are held accountable.

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