delivered the opinion of the Court.
Article 17 of the Warsaw Convention
1
makes air carriers liable for injuries sustained by a passenger “if the accident which caused the damage so sustained took place on board the aircraft or in the course of any of the operations of embarking or disembarking.” We granted certiorari,
rH
On November 16, 1980, respondent Valerie Saks boarded an Air France jetliner in Paris for a 12-hour flight to Los Angeles. The flight went smoothly in all respects until, as the aircraft descended to Los Angeles, Saks felt severe pressure and pain in her left ear. The pain continued after the plane landed, but Saks disembarked without informing any Air France crew member or employee of her ailment. Five days later, Saks consulted a doctor who concluded that she had become permanently deaf in her left ear.
Saks filed suit against Air France in California state court, alleging that her hearing loss was caused by negligent maintenance and operation of the jetliner’s pressurization system. App. 2. The case was removed to the United States District Court for the Central District of California. After extensive *395 discovery, Air France moved for summary judgment on the ground that respondent could not prove that her injury was caused by an “accident” within the meaning of the Warsaw Convention. The term “accident,” according to Air France, means an “abnormal, unusual or unexpected occurrence aboard the aircraft.” Id., at 9. All the available evidence, including the postflight reports, pilot’s affidavit, and passenger testimony, indicated that the aircraft’s pressurization system had operated in the usual manner. Accordingly, the airline contended that the suit should be dismissed because the only alleged cause of respondent’s injury — normal operation of a pressurization system — could not qualify as an “accident.” In her opposition to the summary judgment motion, Saks acknowledged that “[t]he sole question of law presented ... by the parties is whether a loss of hearing proximately caused by normal operation of the aircraft’s pressurization system is an ‘accident’ within the meaning of Article 17 of the Warsaw Convention . . . .” Id., at 30. She argued that “accident” should be defined as a “hazard of air travel,” and that her injury had indeed been caused by such a hazard.
Relying on precedent which defines the term “accident” in Article 17 as an “unusual or unexpected” happening, see
DeMarines
v.
KLM Royal Dutch Airlines,
Air France is liable to a passenger under the terms of the Warsaw Convention only if the passenger proves that an “accident” was the cause of her injury.
MacDonald
v.
Air Canada,
A
Article 17 of the Warsaw Convention establishes the liability of international air carriers for harm to passengers. Article 18 contains parallel provisions regarding liability for damage to baggage. The governing text of the Convention is in the French language, and we accordingly set forth the French text of the relevant part of Articles 17 and 18 in the margin. 2 The official American translation of this portion of the text, which was before the Senate when it ratified the Convention in 1934, reads as follows: .
“Article 17
“The carrier shall be liable for damage sustained in the event of the death or wounding of a passenger or any other bodily injury suffered by a passenger, if the accident which caused the damage so sustained took place on board the aircraft or in the course of any of the operations of embarking or disembarking.
“Article 18
“(1) The carrier shall be liable for damage sustained in the event of the destruction or loss of, or of damage to, any checked baggage or any goods, if the occurrence *398 which caused the damage so sustained took place during the transportation by air.” 49 Stat. 3018-3019.
Two significant features of these provisions stand out in both the French and the English texts. First, Article 17 imposes liability for injuries to passengers caused by an “accident,” whereas Article 18 imposes liability for destruction or loss of baggage caused by an “occurrence.” This difference in the parallel language of Articles 17 and 18 implies that the drafters of the Convention understood the word “accident” to mean something different than the word “occurrence,” for they otherwise logically would have used the same word in each article. See Goedhuis, supra, at 200-201; M. Milde, The Problems of Liabilities in International Carriage by Air 62 (Caroline Univ. 1963). The language of the Convention accordingly renders suspect the opinion of the Court of Appeals that “accident” means “occurrence.”
Second, the text of Article 17 refers to an accident which caused the passenger’s injury, and not to an accident which is the passenger’s injury. In light of the many senses in which the word “accident” can be used, this distinction is significant. As Lord Lindley observed in 1903:
“The word ‘accident’ is not a technical legal term with a clearly defined meaning. Speaking generally, but with reference to legal liabilities, an accident means any unintended and unexpected occurrence which produces hurt or loss. But it is often used to denote any unintended and unexpected loss or hurt apart from its cause; and if the cause is not known the loss or hurt itself would certainly be called an accident. The word ‘accident’ is also often used to denote both the cause and the effect, no attempt being made to discriminate between them.” Fenton v. J. Thorley & Co., [1903] A. C. 443, 453.
In Article 17, the drafters of the Warsaw Convention apparently did make an attempt to discriminate between “the cause and the effect”; they specified that air carriers would
*399
be liable if an accident
caused
the passenger’s injury. The text of the Convention thus implies that, however we define “accident,” it is the
cause
of the injury that must satisfy the definition rather than the occurrence of the injury alone. American jurisprudence has long recognized this distinction between an accident that is the
cause
of an injury and an injury that is itself an accident. See
Landress
v.
Phoenix Mutual Life Ins. Co.,
While the text of the Convention gives these two clues to the meaning of “accident,” it does not define the term. Nor is the context in which the term is used illuminating. See Note, Warsaw Convention — Air Carrier Liability for Passenger Injuries Sustained Within a Terminal, 45 Ford. L. Rev. 369, 388 (1976) (“The language of Article 17 is stark and undefined”). To determine the meaning of the term “accident” in Article 17 we must consider its French legal meaning. See
Reed
v.
Wiser,
A survey of French cases and dictionaries indicates that the French legal meaning of the term “accident” differs little from the meaning of the term in Great Britain, Germany, or the United States. Thus, while the word “accident” is often
*400
used to refer to the
event
of a person’s injury,
3
it is also sometimes used to describe a
cause
of injury, and when the word is used in this latter sense, it is usually defined as a fortuitous, unexpected, unusual, or unintended event. See 1 Grand Larousse de La Langue Franchise 29 (1971) (defining “accident” as “Evénement fortuit et fácheux, causant des dommages corporels ou materiels”);
Air France
v.
Haddad, Judgment of June 19,1979,
Cour d’appel de Paris, Premiere Chambre Civile, 1979 Revue Frangaise de Droit Aérien 327, 328, appeal rejected,
Judgment of February 16, 1982,
Cour de Cassation, 1982 Bull. Civ. I 63. This parallels British and American jurisprudence. See
Fenton
v.
J. Thorley & Co., supra; Landress
v.
Phoenix Mutual Life Ins. Co., supra; Koehring Co.
v.
American Automobile Ins. Co.,
B
This interpretation of Article 17 is consistent with the negotiating history of the Convention, the conduct of the parties to the Convention, and the weight of precedent in foreign and American courts. In interpreting a treaty it is proper, of course, to refer to the records of its drafting and negotiation.
Choctaw Nation of Indians
v.
United States,
*401 The treaty that became the Warsaw Convention was first drafted at an international conference in Paris in 1925. The protocol resulting from the Paris Conference contained an article specifying: “The carrier is liable for accidents, losses, breakdowns, and delays. It is not liable if it can prove that it has taken reasonable measures designed to pre-empt damage . . . .” 4 The protocol drafted at Paris was revised several times by a committee of experts on air law, 5 and then submitted to a second international conference that convened in Warsaw in 1929. The draft submitted to the conference stated:
“The carrier shall be liable for damage sustained during carriage:
“(a) in the case of death, wounding, or any other bodily injury suffered by a traveler;
“(b) in the case of destruction, loss, or damage to goods or baggage;
“(c) in the case of delay suffered by a traveler, goods, or baggage.” International Conference on Air Law Affecting Air Questions, Minutes, Second International Conference on Private Aeronautical Law, October 4-12, 1929, Warsaw 264-265 (R. Horner & D. Legrez trans. 1975).
Article 22 of this draft, like the original Paris draft, permitted the carrier to avoid liability by proving it had taken reasonable measures to avoid the damage. Id., at 265. None of the early drafts required that an accident cause the passenger’s injury.
*402 At Warsaw, delegates from several nations objected to the application of identical liability rules to both passenger injuries and damage to baggage, and the German delegation proposed separate liability rules for passengers and baggage. Id., at 36. The need for separate rules arose primarily because delegates thought that liability for baggage should commence upon delivery to the carrier, whereas liability for passengers should commence when the passengers later embark upon the aircraft. Id., at 72-74 (statements of French, Swiss, and Italian delegates). The Reporter on the Preliminary Draft of the Convention argued it would be too difficult to draft language specifying this distinction, and that such a distinction would be unnecessary because “Article 22 establishes a very mitigated system of liability for the carrier, and from the moment that the carrier has taken the reasonable measures, he does not answer for the risks, nor for the accidents occur[r]ing to people by the fault of third parties, nor for accidents occur[r]ing for any other cause.” Id., at 77-78 (statement of Reporter De Vos). The delegates were unpersuaded, and a majority voted to have a drafting committee rework the liability provisions for passengers and baggage. Id., at 83.
A few days later, the drafting committee proposed the liability provisions that became Articles 17 and 18 of the Convention. Article 20(1) of the final draft contains the “necessary measures” language which the Reporter believed would shield the carrier from liability for “the accidents occur[r]ing to people by the fault of third parties” and for “accidents occur[r]ing for any other cause.” Nevertheless, the redrafted Article 17 also required as a prerequisite to liability that an accident cause the passenger’s injury, whereas the redrafted Article 18 required only that an occurrence cause the damage to baggage. Although Article 17 and Article 18 as redrafted were approved with little discussion, the President of the drafting committee observed that “given that there are entirely different liability cases: death or wounding, disappear- *403 anee of goods, delay, we have deemed that it would be better to begin by setting out the causes of liability for persons, then for goods and baggage, and finally liability in the case of delay.” Id., at 205 (statement of Delegate Giannini) (emphasis added). This comment at least implies that the addition of language of causation to Articles 17 and 18 had a broader purpose than specification of the time at which liability commenced. It further suggests that the causes of liability for persons were intended to be different from the causes of liability for baggage. The records of the negotiation of the Convention accordingly support what is evident from its text: A passenger’s injury must be caused by an accident, and an accident must mean something different than an “occurrence” on the plane. Like the text of the Convention, however, the records of its negotiation offer no precise definition of “accident.”
Reference to the conduct of the parties to the Convention and the subsequent interpretations of the signatories helps clarify the meaning of the term. At a Guatemala City International Conference on Air Law in 1971, representatives of many of the Warsaw signatories approved an amendment to Article 17 which would impose liability on the carrier for an “event which caused the death or injury” rather than for an “accident which caused” the passenger’s injury, but would exempt the carrier from liability if the death or injury resulted “solely from the state of health of the passenger.” International Civil Aviation Organization, 2 Documents of the International Conference on Air Law, Guatemala City, ICAO Doc. 9040-LC/167-2, p. 189 (1972). The Guatemala City Protocol of 1971 and the Montreal Protocols Nos. 3 and 4 of 1975 include this amendment, see S. Exec. Rep. No. 98-1 (1983), but have yet to be ratified by the Senate, and therefore do .not govern the disposition of this case. The statements of the delegates at Guatemala City indicate that they viewed the switch from “accident” to “event” as expanding the scope of carrier liability to passengers. The Swedish *404 Delegate, for example, in referring to the choice between the words “accident” and “event,” emphasized that the word “accident” is too narrow because a carrier might be found liable for “other acts which could not be considered as accidents.” See International Civil Aviation Organization, 1 Minutes of the International Conference on Air Law, ICAO Doc. 9040-LC/167-1, p. 34 (1972). See also Mankiewicz, Warsaw Convention: The 1971 Protocol of Guatemala City, 20 Am. J. Comp. L. 335, 337 (1972) (noting that changes in Article 17 were intended to establish “strict liability”).
In determining precisely what causes can be considered accidents, we “find the opinions of our sister signatories to be entitled to considerable weight.”
Benjamins
v.
British European Airways,
Ill
We conclude that liability under Article 17 of the Warsaw Convention arises only if a passenger’s injury is caused by an unexpected or unusual event or happening that is external to the passenger. This definition should be flexibly applied after assessment of all the circumstances surrounding a passenger’s injuries.
Maugnie, supra,
at 1262. For example, lower courts in this country have interpreted Article 17 broadly enough to encompass torts committed by terrorists or fellow passengers. See
Evangelinos
v.
Trans World Airlines, Inc.,
We recognize that any standard requiring courts to distinguish causes that are “accidents” from causes that are “occurrences” requires drawing a line, and we realize that “reasonable [people] may differ widely as to the place where the line should fall.”
Schlesinger
v.
Wisconsin,
Our duty to enforce the “accident” requirement of Article 17 cannot be circumvented by reference to the Montreal Agreement of 1966. It is true that in most American cases the Montreal Agreement expands carrier liability by requiring airlines to waive their right under Article 20(1) of the Warsaw Convention to defend claims on the grounds that
*407
they took all necessary measures to avoid the passenger’s injury or that it was impossible to take such measures. Because these “due care” defenses are waived by the Montreal Agreement, the Court of Appeals and some commentators have characterized the Agreement as imposing “absolute” liability on air carriers. See Lowenfeld & Mendelsohn,
Nor can we escape our duty to enforce Article 17 by reference to the equation of “accident” with “occurrence” in Annex 13 to the Convention on International Civil Aviation. The definition in Annex 13 and the corresponding Convention expressly apply to aircraft accident investigations, and not to principles of liability to passengers under the Warsaw Convention. See B. Cheng, The Law of International Air Transport 106-165 (1962).
*408
Finally, respondent suggests an independent ground supporting the Court of Appeals’ reversal of the summary judgment against her. She argues that her original complaint alleged a state cause of action for negligence independent of the liability provisions of the Warsaw Convention, and that her state negligence action can go forward if the Warsaw liability rules do not apply. Expressing no view on the merits of this contention, we note that it is unclear from the record whether the issue was raised in the Court of Appeals. We leave the disposition of this claim to the Court of Appeals in the first instance. See
Hoover
v.
Ronwin,
The judgment of the Court of Appeals is reversed, and the case is remanded for further proceedings consistent with this opinion.
It is so ordered.
Notes
Convention for the Unification of Certain Rules Relating to International Transportation by Air, Oct. 12, 1929, 49 Stat. 3000, T. S. No. 876 (1934), note following 49 U. S. C. App. § 1502.
“Article 17
“Le transporteur est responsable du dommage survenu en cas de mort, de blessure ou de toute autre lésion corporelle subie par un voyageur lorsque l’accident qui a causé le dommage s’est produit á bord de l’aéronef ou au cours de toutes opérations d’embarquement et de débarquement.
“Article 18
“(1) Le transporteur est responsable du dommage survenu en eas destruction, perte ou avarie de bagages enregistrés ou de marchandises lorsque l’événement qui a causé le dommage s’est produit pendant le transport aérien.” 49 Stat. 3005 (emphasis added).
Article 36 of the Convention recites that it is drawn in French. Id., at 3008.
See, e. g., M. LeGrand, Dictionnaire Usuel de Droit 8 (1931) (defining “accident” as “Evénement fortuit et malheureux qui ouvre á la victime, soit par suite de l’imprévoyance ou de la négligence d’une personne, soit en vertu du ‘risque professionel,’ droit á une réparation pécuniaire”).
“Le transporteur est responsable des accidents, pertes, avaries et retards. II n’est pas responsable s’il prouve avoir pris les mesures raisonnables pour éviter le dommage . . . .” [1925 Paris] Conférence Internationale de Droit Privé Aérien 87 (1936).
See Report of the Second Session, International Technical Committee of Legal Experts on Air Questions (1927); Report of the Third Session, International Technical Committee of Legal Experts on Air Questions (1928).
