delivered the opinion of the Court.
The petitioner, Western Air Lines, Inc., requires that its flight engineers retire at age 60. Although the Age Discrimination in Employment Act of 1967 (ADEA), 29 U. S. C. *403§§621-634, generally prohibits mandatory retirement before age 70, the Act provides an exception “where age is a bona fide occupational qualification [BFOQ] reasonably necessary to the normal operation of the particular business.”1 A jury concluded that Western’s mandatory retirement rule did not qualify as a BFOQ even though it purportedly was adopted for safety reasons. The question here is whether the jury was properly instructed on the elements of the BFOQ defense.2
I
In its commercial airline operations, Western operates a variety of aircraft, including the Boeing 727 and the McDonnell-Douglas DC-10. These aircraft require three crew members in the cockpit: a captain, a first officer, and a flight engineer. “The ‘captain’ is the pilot and controls the aircraft. He is responsible for all phases of its operation. The ‘first officer’ is the copilot and assists the captain. The ‘flight engineer’ usually monitors a side-facing instrument panel. He does not operate the flight controls unless the captain and the first officer become incapacitated.” Trans World Airlines, Inc. v. Thurston, 469 U. S. 111, 114 (1985).
*404A regulation of the Federal Aviation Administration (FAA) prohibits any person from serving as a pilot or first officer on a commercial flight “if that person has reached his 60th birthday.” 14 CFR § 121.383(c) (1985). The FAA has justified the retention of mandatory retirement for pilots on the theory that “incapacitating medical events” and “adverse psychological, emotional, and physicial changes” occur as a consequence of aging. “The inability to detect or predict with precision an individual’s risk of sudden or subtle incapacitation, in the face of known age-related risks, counsels against relaxation of the rule.” 49 Fed. Reg. 14695 (1984). See also 24 Fed. Reg. 9776 (1959).
At the same time, the FAA has refused to establish a mandatory retirement age for flight engineers. “While a flight engineer has important duties which contribute to the safe operation of the airplane, he or she may not assume the responsibilities of the pilot in command.” 49 Fed. Reg., at 14694. Moreover, available statistics establish that flight engineers have rarely been a contributing cause or factor in commercial aircraft “accidents” or “incidents.” Ibid.
In 1978, respondents Criswell and Starley were captains operating DC-10s for Western. Both men celebrated their 60th birthdays in July 1978. Under the collective-bargaining agreement in effect between Western and the union, cockpit crew members could obtain open positions by bidding in order of seniority.3 In order to avoid mandatory retirement *405under the FAA’s under-age-60 rule for pilots, Criswell and Starley applied for reassignment as flight engineers. Western denied both requests, ostensibly on the ground that both employees were members of the company’s retirement plan which required all crew members to retire at age 60.4 For the same reason, respondent Ron, a career flight engineer, was also retired in 1978 after his 60th birthday.
Mandatory retirement provisions similar to those contained in Western’s pension plan had previously been upheld under the ADEA. United Air Lines, Inc. v. McMann, 434 U. S. 192 (1977). As originally enacted in 1967, the Act provided an exception to its general proscription of age discrimination for any actions undertaken “to observe the terms of a. . . bona fide employee benefit plan such as a retirement, pension, or insurance plan, which is not a subterfuge to evade the purposes of this Act.”5 In April 1978, however, Congress amended the statute to prohibit employee benefit plans from requiring the involuntary retirement of any employee because of age.6
Criswell, Starley, and Ron brought this action against Western contending that the under-age-60 qualification for *406the position of flight engineer violated the ADEA. In the District Court, Western defended, in part, on the theory that the age-60 rule is a BFOQ “reasonably necessary” to the safe operation of the airline.7 All parties submitted evidence concerning the nature of the flight engineer’s tasks, the physiological and psychological traits required to perform them, and the availability of those traits among persons over age 60.
As the District Court summarized, the evidence at trial established that the flight engineer’s “normal duties are less critical to the safety of flight than those of a pilot.” 514 F. Supp. 384, 390 (CD Cal. 1981). The flight engineer, however, does have critical functions in emergency situations and, of course, might cause considerable disruption in the event of his own medical emergency.
The actual capabilities of persons over age 60, and the ability to detect disease or a precipitous decline in their faculties, were the subject of conflicting medical testimony. Western’s expert witness, a former FAA Deputy Federal Air Surgeon,8 was especially concerned about the possibility of a “cardiovascular event” such as a heart attack. He testified that “with advancing age the likelihood of onset of disease increases and that in persons over age 60 it could not be predicted whether and when such diseases would occur.” Id., at 389.
The plaintiffs’ experts, on the other hand, testified that physiological deterioration is caused by disease, not aging, and that “it was feasible to determine on the basis of individual medical examinations whether flight deck crew members, including those over age 60, were physically qualified to con*407tinue to fly.” Ibid. These conclusions were corroborated by the nonmedical evidence:
“The record also reveals that both the FAA and the airlines have been able to deal with the health problems of pilots on an individualized basis. Pilots who have been grounded because of alcoholism or cardiovascular disease have been recertified by the FAA and allowed to resume flying. Pilots who were unable to pass the necessary examination to maintain their FAA first class medical certificates, but who continued to qualify for second class medical certificates were allowed to ‘downgrade’ from pilot to [flight engineer]. There is nothing in the record to indicate that these flight deck crew members are physically better able to perform their duties than flight engineers over age 60 who have not experienced such events or that they are less likely to become incapacitated.” Id., at 390.
Moreover, several large commercial airlines have flight engineers over age 60 “flying the line” without any reduction in their safety record. Ibid.
The jury was instructed that the “BFOQ defense is available only if it is reasonably necessary to the normal operation or essence of defendant’s business.” Tr. 2626. The jury was informed that “the essence of Western’s business is the safe transportation of their passengers.” Ibid. The jury was also instructed:
“One method by which defendant Western may establish a BFOQ in this case is to prove:
“(1) That in 1978, when these plaintiffs were retired, it was highly impractical for Western to deal with each second officer over age 60 on an individualized basis to determine his particular ability to perform his job safely; and
“(2) That some second officers over age 60 possess traits of a physiological, psychological or other nature *408which preclude safe and efficient job performance that cannot be ascertained by means other than knowing their age.
“In evaluating the practicability to defendant Western of dealing with second officers over age 60 on an individualized basis, with respect to the medical testimony, you should consider the state of the medical art as it existed in July 1978.” Id., at 2627.
The jury rendered a verdict for the plaintiffs, and awarded damages. After trial, the District Court granted equitable relief, explaining in a written opinion why it found no merit in Western’s BFOQ defense to the mandatory retirement rule. 514 F. Supp., at 389-391.9
On appeal, Western made various arguments attacking the verdict and judgment below, but the Court of Appeals affirmed in all respects. 709 F. 2d 544 (CA9 1983). In particular, the Court of Appeals rejected Western’s contention that the instruction on the BFOQ defense was insufficiently deferential to the airline’s legitimate concern for the safety of its passengers. Id., at 549-551. We granted certiorari to consider the merits of this question. 469 U. S. 815 (1984).10
*409h-i hH
Throughout the legislative history of the ADEA, one empirical fact is repeatedly emphasized: the process of psychological and physiological degeneration caused by aging varies with each individual. “The basic research in the field of aging has established that there is a wide range of individual physical ability regardless of age.”11 As a result, many older American workers perform at levels equal or superior to their younger colleagues.
In 1965, the Secretary of Labor reported to Congress that despite these well-established medical facts there “is persistent and widespread use of age limits in hiring that in a great many cases can be attributed only to arbitrary discrimination against older workers on the basis of age and regardless of ability.”12 Two years later, the President recommended that Congress enact legislation to abolish arbitrary age limits on *410hiring. Such limits, the President declared, have a devastating effect on the dignity of the individual and result in a staggering loss of human resources vital to the national economy.13
After further study,14 Congress responded with the enactment of the ADEA. The preamble declares that the purpose of the ADEA is “to promote employment of older persons based on their ability rather than age [and] to prohibit arbitrary age discrimination in employment.” 81 Stat. 602, 29 U. S. C. § 621(b). Section 4(a)(1) makes it “unlawful for an employer ... to fail or refuse to hire or to discharge any individual or otherwise discriminate against any individual with respect to his compensation, terms, conditions, or privileges of employment, because of such individual’s age.” 81 Stat. 603, 29 U. S. C. § 623(a)(1). This proscription presently applies to all persons between the ages of 40 and 70. 29 U. S. C. § 631(a).
The legislative history of the 1978 Amendments to the ADEA makes quite clear that the policies and substantive provisions of the Act apply with especial force in the case of mandatory retirement provisions. The House Committee on Education and Labor reported:
“Increasingly, it is being recognized that mandatory retirement based solely upon age is arbitrary and that chronological age alone is a poor indicator of ability to perform a job. Mandatory retirement does not take *411into consideration actual differing abilities and capacities. Such forced retirement can cause hardships for older persons through loss of roles and loss of income. Those older persons who wish to be re-employed have a much more difficult time finding a new job than younger persons.
“Society, as a whole, suffers from mandatory retirement as well. As a result of mandatory retirement, skills and experience are lost from the work force resulting in reduced GNP. Such practices also add a burden to Government income maintenance programs such as social security.”15
In the 1978 Amendments, Congress narrowed an exception to the ADEA which had previously authorized involuntary retirement under limited circumstances. See supra, at 405.
In both 1967 and 1978, however, Congress recognized that classifications based on age, like classifications based on religion, sex, or national origin, may sometimes serve as a necessary proxy for neutral employment qualifications essential to the employer’s business. The diverse employment situations in various industries, however, forced Congress to adopt a “case-by-case basis ... as the underlying rule in the administration of the legislation.” H. R. Rep. No. 805, 90th Cong., 1st Sess., 7 (1967), Legislative History 80.16 Congress offered only general guidance on when an age clas*412sification might be permissible by borrowing a concept and statutory language from Title VII of the Civil Rights Act of 196417 and providing that such a classification is lawful “where age is a bona fide occupational qualification reasonably necessary to the normal operation of the particular business.” 29 U. S. C. § 623(f)(1).
Shortly after the passage of the Act, the Secretary of Labor, who was at that time charged with its enforcement, adopted regulations declaring that the BFOQ exception to the ADEA has only “limited scope and application” and “must be construed narrowly.” 33 Fed. Reg. 9172 (1968), 29 CFR §860.102(b) (1984). The Equal Employment Opportunity Commission (EEOC) adopted the same narrow construction of the BFOQ exception after it was assigned authority for enforcing the statute. 46 Fed. Reg. 47727 (1981), 29 CFR § 1625.6 (1984). The restrictive language of the statute and the consistent interpretation of the administrative agencies charged with enforcing the statute convince us that, like its Title VII counterpart, the BFOQ exception “was in fact meant to be an extremely narrow exception to the general prohibition” of age discrimination contained in the ADEA. Dothard v. Rawlinson, 433 U. S. 321, 334 (1977).
HH 1 — 1 H-1
In Usery v. Tamiami Trail Tours, Inc., 531 F. 2d 224 (1976), the Court of Appeals for the Fifth Circuit was called upon to evaluate the merits of a BFOQ defense to a claim of age discrimination. Tamiami Trail Tours, Inc., had a policy of refusing to hire persons over age 40 as intercity bus drivers. At trial, the bus company introduced testimony supporting its theory that the hiring policy was a BFOQ based *413upon safety considerations — the need to employ persons who have a low risk of accidents. In evaluating this contention, the Court of Appeals drew on its Title VII precedents, and concluded that two inquiries were relevant.
First, the court recognized that some job qualifications may be so peripheral to the central mission of the employer’s business that no age discrimination can be “reasonably necessary to the normal operation of the particular business.”18 29 U. S. C. § 623(f)(1). The bus company justified the age qualification for hiring its drivers on safety considerations, but the court concluded that this claim was to be evaluated under an objective standard:
“[T]he job qualifications which the employer invokes to justify his discrimination must be reasonably necessary to the essence of his business — here, the safe transportation of bus passengers from one point to another. The greater the safety factor, measured by the likelihood of harm and the probable severity of that harm in case of an accident, the more stringent may be the job qualifications designed to insure safe driving.” 531 F. 2d, at 236.
This inquiry “adjusts to the safety factor” by ensuring that the employer’s restrictive job qualifications are “reasonably necessary” to further the overriding interest in public safety. Ibid. In Tamiami, the court noted that no one had seriously *414challenged the bus company’s safety justification for hiring drivers with a low risk of having accidents.
Second, the court recognized that the ADEA requires that age qualifications be something more than “convenient” or “reasonable”; they must be “reasonably necessary ... to the particular business,” and this is only so when the employer is compelled to rely on age as a proxy for the safety-related job qualifications validated in the first inquiry.19 This showing could be made in two ways. The employer could establish that it “‘had reasonable cause to believe, that is, a factual basis for believing, that all or substantially all [persons over the age qualifications] would be unable to perform safely and efficiently the duties of the job involved.’”20 In Tamiami, the employer did not seek to justify its hiring qualification under this standard.
Alternatively, the employer could establish that age was a legitimate proxy for the safety-related job qualifications by proving that it is “ ‘impossible or highly impractical’ ” to deal with the older employees on an individualized basis.21 “One method by which the employer can carry this burden is to establish that some members of the discriminated-against class possess a trait precluding safe and efficient job performance *415that cannot be ascertained by means other than knowledge of the applicant’s membership in the class.” Id., at 235. In Tamiami, the medical evidence on this point was conflicting, but the District Court had found that individual examinations could not determine which individuals over the age of 40 would be unable to operate the buses safely. The Court of Appeals found that this finding of fact was not “clearly erroneous,” and affirmed the District Court’s judgment for the bus company on the BFOQ defense. Id., at 238.
Congress, in considering the 1978 Amendments, implicitly endorsed the two-part inquiry identified by the Fifth Circuit in the Tamiami case. The Senate Committee Report expressed concern that the amendment prohibiting mandatory retirement in accordance with pension plans might imply that mandatory retirement could not be a BFOQ:
“For example, in certain types of particularly arduous law enforcement activity, there may be a factual basis for believing that substantially all employees above a specified age would be unable to continue to perform safely and efficiently the duties of their particular jobs, and it may be impossible or impractical to determine through medical examinations, periodic reviews of current job performance and other objective tests the employees’ capacity or ability to continue to perform the jobs safely and efficiently.
“Accordingly, the committee adopted an amendment to make it clear that where these two conditions are satisfied and where such a bona fide occupational qualification has therefore been established, an employer may lawfully require mandatory retirement at that specified age.” S. Rep. No. 95-493, pp. 10-11 (1977), Legislative History 443-444.
The amendment was adopted by the Senate, but deleted by the Conference Committee because it “neither added to nor *416worked any change upon present law.”22 H. R. Conf. Rep. No. 95-950, p. 7 (1978), Legislative History 518.
Every Court of Appeals that has confronted a BFOQ defense based on safety considerations has analyzed the problem consistently with the Tamiami standard.23 An EEOC regulation embraces the same criteria.24 Considering the narrow language of the BFOQ exception, the parallel treatment of such questions under Title VII, and the uniform application of the standard by the federal courts, the EEOC, and Congress, we conclude that this two-part inquiry prop*417erly identifies the relevant considerations for resolving a BFOQ defense to an age-based qualification purportedly justified by considerations of safety.
hH
In the trial court, Western preserved an objection to any instruction in the Tamiami mold, claiming that “any instruction pertaining to the statutory phrase ‘reasonably necessary to the normal operation of [defendant’s] business’... is irrelevant to and confusing for the deliberations of the jury.”25 Western proposed an instruction that would have allowed it to succeed on the BFOQ defense by proving that “in 1978, when these plaintiffs were retired, there existed a rational basis in fact for defendant to believe that use of [flight engineers] over age 60 on its DC-10 airliners would increase the likelihood of risk to its passengers.”26 The proposed instruction went on to note that the jury might rely on the FAA’s age-60 rule for pilots to establish a BFOQ under this standard “without considering any other evidence.”27 It also noted that the medical evidence submitted by the parties might provide a “rational basis in fact.”
On appeal, Western defended its proposed instruction, and the Court of Appeals soundly rejected it. 709 F. 2d, at • 549-551. In this Court, Western slightly changes its course. *418The airline now acknowledges that the Tamiami standard identifies the relevant general inquiries that must be made in evaluating the BFOQ defense. However, Western claims that in several respects the instructions given below were insufficiently protective of public safety. Western urges that we interpret or modify the Tamiami standard to weigh these concerns in the balance.
Reasonably Necessary Job Qualifications
Western relied on two different kinds of job qualifications to justify its mandatory retirement policy. First, it argued that flight engineers should have a low risk of incapacitation or psychological and physiological deterioration. At this vague level of analysis respondents have not seriously disputed — nor could they — that the qualification of good health for a vital crew member is reasonably necessary to the essence of the airline’s operations. Instead, they have argued that age is not a necessary proxy for that qualification.
On a more specific level, Western argues that flight engineers must meet the same stringent qualifications as pilots, and that it was therefore quite logical to extend to flight engineers the FAA’s age-60 retirement rule for pilots. Although the FAA’s rule for pilots, adopted for safety reasons, is relevant evidence in the airline’s BFOQ defense, it is not to be accorded conclusive weight. Johnson v. Mayor and City Council of Baltimore, ante, at 370-371. The extent to which the rule is probative varies with the weight of the evidence supporting its safety rationale and “the congruity between the . . . occupations at issue.” Ante, at 371. In this case, the evidence clearly established that the FA A, Western, and other airlines all recognized that the qualifications for a flight engineer were less rigorous than those required for a pilot.28
*419In the absence of persuasive evidence supporting its position, Western nevertheless argues that the jury should have been instructed to defer to “Western’s selection of job qualifications for the position of [flight engineer] that are reasonable in light of the safety risks.” Brief for Petitioner 30. This proposal is plainly at odds with Congress’ decision, in adopting the ADEA, to subject such management decisions to a test of objective justification in a court of law. The BFOQ standard adopted in the statute is one of “reasonable necessity,” not reasonableness.
In adopting that standard, Congress did not ignore the public interest in safety. That interest is adequately reflected in instructions that track the language of the statute. When an employer establishes that a job qualification has been carefully formulated to respond to documented concerns for public safety, it will not be overly burdensome to persuade a trier of fact that the qualification is “reasonably necessary” to safe operation of the business. The uncertainty implicit in the concept of managing safety risks always makes it “reasonably necessary” to err on the side of caution in a close case.29 The employer cannot be expected to establish the risk of an airline accident “to a certainty, for certainty would require running the risk until a tragic accident would *420prove that the judgment was sound.” Usery v. Tamiami Trail Tours, Inc., 531 F. 2d, at 238. When the employer’s argument has a credible basis in the record, it is difficult to believe that a jury of laypersons — many of whom no doubt have flown or could expect to fly on commercial air carriers— would not defer in a close case to the airline’s judgment. Since the instructions in this case would not have prevented the airline from raising this contention to the jury in closing argument, we are satisfied that the verdict is a consequence of a defect in Western’s proof rather than a defect in the trial court’s instructions.30
Western’s Statutory Safety Obligation
The instructions defined the essence of Western’s business as “the safe transportation of their passengers.” Tr. 2626. Western complains that this instruction was defective because it failed to inform the jury that an airline must conduct its operations “with the highest possible degree of safety.”31
Jury instructions, of course, “may not be judged in artificial isolation,” but must be judged in the “context of the overall charge” and the circumstances of the case. See Cupp v. Naughten, 414 U. S. 141, 147 (1973). In this case, the instructions characterized safe transportation as the “essence” *421of Western’s business and specifically referred to the importance of “safe and efficient job performance” by flight engineers. Tr. 2627. Moreover, in closing argument counsel pointed out that because “safety is the essence of Western’s business,” the airline strives for “the highest degree possible of safety.”32 Viewing the record as a whole, we are satisfied that the jury’s attention was adequately focused on the importance of safety to the operation of Western’s business. Cf. United States v. Park, 421 U. S. 658, 674 (1975).
Age as a Proxy for Job Qualifications
Western contended below that the ADEA only requires that the employer establish “a rational basis in fact” for believing that identification of those persons lacking suitable qualifications cannot occur on an individualized basis.33 This “rational basis in fact” standard would have been tantamount to an instruction to return a verdict in the defendant’s favor. Because that standard conveys a meaning that is significantly different from that conveyed by the statutory phrase “reasonably necessary,” it was correctly rejected by the trial court.34
*422Western argues that a “rational basis” standard should be adopted because medical disputes can never be proved “to a certainty” and because juries should not be permitted “to resolve bona fide conflicts among medical experts respecting the adequacy of individualized testing.” Reply Brief for Petitioner 9, n. 10. The jury, however, need not be convinced beyond all doubt that medical testing is impossible, but only that the proposition is true “on a preponderance of the evidence.” Moreover, Western’s attack on the wisdom of assigning the resolution of complex questions to 12 laypersons is inconsistent with the structure of the ADEA. Congress expressly decided that problems involving age discrimination in employment should be resolved on a “case-by-case basis” by proof to a jury.35
The “rational basis” standard is also inconsistent with the preference for individual evaluation expressed in the language and legislative history of the ADEA.36 Under the Act, employers are to evaluate employees between the ages of 40 and 70 on their merits and not their age. In the BFOQ defense, Congress provided a limited exception to this general principle, but required that employers validate any discrimination as “reasonably necessary to the normal operation of the particular business.” It might well be “rational” to require mandatory retirement at any age less than 70, but that result would not comply with Congress’ direction that employers must justify the rationale for the age chosen. Unless an employer can establish a substantial basis for believing that all or nearly all employees above an age lack the qualifications required for the position, the age selected for mandatory retirement less than 70 must be an age at which it *423is highly impractical for the employer to insure by individual testing that its employees will have the necessary qualifications for the job.
Western argues that its lenient standard is necessary because “where qualified experts disagree as to whether persons over a certain age can be dealt with on an individual basis, an employer must be allowed to resolve that controversy in a conservative manner.” Reply Brief for Petitioner 8-9. This argument incorrectly assumes that all expert opinion is entitled to equal weight, and virtually ignores the function of the trier of fact in evaluating conflicting testimony. In this case, the jury may well have attached little weight to the testimony of Western’s expert witness. See supra, at 406, and n. 8. A rule that would require the jury to defer to the judgment of any expert witness testifying for the employer, no matter how unpersuasive, would allow some employers to give free reign to the stereotype of older workers that Congress decried in the legislative history of the ADEA.
When an employee covered by the Act is able to point to reputable businesses in the same industry that choose to eschew reliance on mandatory retirement earlier than age 70, when the employer itself relies on individualized testing in similar circumstances, and when the administrative agency with primary responsibility for maintaining airline safety has determined that individualized testing is not impractical for the relevant position, the employer’s attempt to justify its decision on the basis of the contrary opinion of experts— solicited for the purposes of litigation — is hardly convincing on any objective standard short of complete deference. Even in cases involving public safety, the ADEA plainly does not permit the trier of fact to give complete deference to the employer’s decision.
The judgment of the Court of Appeals is
Affirmed.
Justice Powell took no part in the decision of this case.