Opinion for the Court filed by Circuit Judge HARRY T. EDWARDS.
HARRY T. EDWARDS, Circuit Judge:
The Telecommunications Research & Action Center (“TRAC”) and several other not-for-profit corporations and public interest groups petition this court for a writ of mandamus to compel the Federal Communications Commission (“FCC” or “the Commission”) to decide certain unresolved matters now pending before the agency. The essence of TRAC’s claim is that the FCC has unreasonably delayed determining whether American Telephone and Telegraph Company (“AT&T”) must reimburse ratepayers for two separate instances of allegedly unlawful overcharges. The first instance relates to the rate of return earned by AT&T and the Bell System on interstate and foreign services furnished during 1978. The second concerns the treatment of expenses incurred by AT&T’s manufacturing subsidiary, Western Electric, in its development of “customer premises equipment” (“CPE”)1 during 1980-1982.
The most important question that we face in our consideration of this interlocutory appeal is a threshold jurisdictional issue. Our resolution of this issue is of particular significance because it is dispositive of both the instant case and a similar appeal involving the Civil Aeronautics Board that was argued before this panel on the same day as this case. See note 22 infra.
Our jurisdictional inquiry focuses on whether a petition to compel unreasonably delayed agency action properly lies in this court or in the District Court, or whether the two courts have concurrent jurisdiction, when any final agency action in the matter would be directly reviewable only in the Court of Appeals. Although we find the precedent in this circuit to be less than clear on this question, we conclude that, where a statute commits final agency action to review by the Court of Appeals, the appellate court has exclusive jurisdiction to hear suits seeking relief that might affect its future statutory power of review.
On the merits of the instant appeal, we decide that, because the agency has assured us that it is now moving expeditiously to resolve the pending overcharge claims, we need not determine whether the cited delays are so egregious as to warrant mandamus. The court, however, will retain jurisdiction over this case until final disposition by the agency.
[225]*225I. Background
A. The Rate of Return on Interstate and Foreign Services in 1978
In 1976, acting under the ratemaking authority conferred by 47 U.S.C. § 205(a), the FCC set the maximum rate of return for AT&T interstate and foreign operations at 9.5 percent, with a .5 percent additional margin to encourage productivity and efficiency.2 The Commission agreed not to reduce AT&T’s interstate rates provided that its overall rate of return did not exceed ten percent.3 In order “to fully protect the public,” however, the FCC required that AT&T maintain an accounting of its relevant revenues to facilitate refunds if an excessive rate of return should occur.4
AT&T’s 1978 interstate rate of return was either 10.22, 10.1, 10.02, or 9.89 percent, depending on the methodology used to calculate it.5 On July 20, 1979, the petitioners filed a Petition for Enforcement of Accounting with the FCC in which they requested that the Commission determine whether AT&T had received excess revenues and, if so, that the FCC order appropriate relief to the ratepayers.6 Rather than acting directly on this petition, the Commission issued a Notice of Inquiry on October 1, 1979, soliciting comments on several issues related to AT&T’s earnings.7 Both comments and reply comments were filed by the end of 1979. The Commission has taken no further action during the almost five years since the filing of comments.
Representative Timothy Wirth, Chairman of the Subcommittee on Telecommunications, Consumer Protection and Finance of the House Committee on Energy and Commerce, has twice written to the FCC to inquire about the unexplained delay in agency action. In 1981, FCC officials responded that they expected a staff recommendation that fall.8 However, no such recommendation was produced. In the spring of 1984, agency officials modified their response and estimated that a staff recommendation would be issued that summer.9 The agency failed on this commitment, too. Now, in the face of this court action, the Commission has recently indicated that it plans to resolve the matter on or before November 30, 1984.10
B. The Treatment of CPE Expenses
In May of 1980, the FCC decided that CPE and enhanced telecommunications services 11 should no longer be regulated12 [226]*226under Title II of the Communications Act.13 It is unnecessary to detail here the effects of this order on ratemaking and carrier accounting. It suffices to note that, in order to shield the regulated market from costs appropriately allocated to the competitive market and from anticompetitive activities, the Commission required AT&T to create a separate subsidiary to act in the enhanced services and CPE markets.14 The FCC also required that all costs associated with competitive activities, such as CPE development costs, be charged solely to this subsidiary, not passed along to the regulated ratepayer.15
Between May 1980, and January of 1983, Western Electric spent about $500 million developing CPE. Because these development costs were expensed as they were incurred, the Commission, in an order dated November 10,1982, expressed concern that between 1980 and 1982 regulated service ratepayers might have impermissibly contributed to recovery of these development expenses. But because the FCC concluded that it could not determine from the existing record whether ratepayer reimbursement for these expenses was warranted, it ordered AT&T to provide it with additional information.16 Due to the importance of this question and because of the significant amount of money involved the FCC also invited public comments.17 AT&T filed its comments in December of 1982 and other comments were filed in January and February 1983.18
On November 15, 1983, petitioners Florida Consumers Federation and others filed a Petition for Intervention and Expeditious Resolution.19 On May 22, 1984, Chairman Wirth inquired about the status of this matter and was told that action was expected during the summer of 1984.20 The Commission now says it will act with respect to the ratemaking treatment of these CPE development expenses on or before June 28, 1985.21 To date, though, the Commission has not acted, either on the petition or on its own inquiry into Western Electric’s CPE development expenses.
II. Jurisdiction
As an initial matter, this case raises two significant and recurrent jurisdictional questions. First, where a statute commits final agency action to review by the Court of Appeals, does that court have jurisdiction to hear suits seeking relief that would affect its future statutory power of review? Second, if the Court of Appeals does have jurisdiction, is that jurisdiction exclusive or concurrent with that of the District Courts?22
We recognize that our precedent concerning jurisdiction over interlocutory appeals from agency action (or inaction) is somewhat inconsistent and may be confusing for litigants attempting to select the proper [227]*227forum for these claims.23 We are convinced that this state of disarray in which we find the law is the product of innocent inadvertence, sometimes attributable to a desire by the court and parties to promptly resolve claims of unreasonable delay, and sometimes attributable to a failure by the parties to raise or to pursue jurisdictional inquiries. Nevertheless, “[¡jurisdiction is, of necessity, the first issue for an Article III court. The federal courts are courts of limited jurisdiction, and they lack the power to presume the existence of jurisdiction in order to dispose of a case on any other grounds.” Tuck v. Pan American Health Organization, 668 F.2d 547, 549 (D.C.Cir.1981). We are therefore obliged to consider and finally resolve the question pertaining to the jurisdiction of the Court of Appeals to hear claims of the sort raised in this case and in the companion ALPA case. See note 22, supra. In deciding this issue, for the reasons hereafter enumerated, we hold that where a statute commits review of agency action .to the Court of Appeals, any suit seeking relief that might affect the Circuit Court’s future jurisdiction is subject to the exclusive review of the Court of Appeals.24
A. The Basis of Our Jurisdiction
We think it is clear — and no party disputes this point — that the statutory commitment of review of FCC action to the Court of Appeals, read in conjunction with the All Writs Act, 28 U.S.C. § 1651(a) (1982), affords this court jurisdiction over claims of unreasonable Commission delay. Exclusive jurisdiction over review of final FCC orders is vested in the Court of Appeals by 28 U.S.C. § 2842(1) (1982)25 and 47 U.S.C. § 402(a) (1982).26 See also FCC v. ITT World Communications, Inc. (“ITT”), — U.S. -, 104 S.Ct. 1936, 1939, 80 L.Ed.2d 480 (1984). Here, of course, there is no final order — indeed, the lack of a final order is the very gravamen of the petitioners’ complaint. This lack of finality, however, does not automatically preclude our jurisdiction.27
[228]*228The All Writs Act provides that “the Supreme Court and all courts established by an Act of Congress may issue all writs necessary or appropriate in aid of their respective jurisdictions ____” 28 U.S.C. § 1651(a). While it is firmly established that section 1651 does not expand the jurisdiction of a court, see, e.g., 9 J. Moore, Moore’s Federal Practice § 110.26 at 282 (2d ed.1983), it is equally well settled that “the authority of the appellate court ‘is not confined to the issuance of writs in aid of jurisdiction already acquired by appeal but extends to those cases which are within its appellate jurisdiction although no appeal has been perfected.’ ” Federal Trade Commission v. Dean Foods Co., 384 U.S. 597, 603-04, 86 S.Ct. 1738, 1742-43, 16 L.Ed.2d 802 (1966) (quoting Roche v. Evaporated Milk Association, 319 U.S. 21, 25, 63 S.Ct. 938, 941, 87 L.Ed. 1185 (1943)). This authority extends to support an ultimate power of review, even though it is not immediately and directly involved. United States v. United States District Court, 334 U.S. 258, 263, 68 S.Ct. 1035, 1037, 92 L.Ed. 1351 (1948). In other words, section 1651(a) empowers a federal court to issue writs of mandamus necessary to protect its prospective jurisdiction. Dean Foods, 384 U.S. at 603-04, 86 S.Ct. at 1742-43; United States District Court, 334 U.S. at 263, 68 S.Ct. at 1037; Potomac Electric Power Co. v. ICC (“PEPCO”), 702 F.2d 1026, 1032 (D.C.Cir.1983); Board of Governors v. Transamerica Corp., 184 F.2d 311, 315 (9th Cir.), cert. denied, 340 U.S. 883, 71 S.Ct. 197, 95 L.Ed. 641 (1950).28 Because the statutory obligation of a Court of Appeals to review on the merits may be defeated by an agency that fails to resolve disputes, a Circuit Court may resolve claims of unreasonable delay in order to protect its future jurisdiction. Environmental Defense Fund, Inc. v. Ruckelshaus, 439 F.2d 584, 593 (D.C.Cir.1971); see also Dean Foods, 384 U.S. at 603, 86 S.Ct. at 1742 (quoting McClellan v. Carland, 217 U.S. 268, 280, 30 S.Ct. 501, 504, 54 L.Ed. 762 (1910) (“ ‘[w]e think it the true rule that where a case is within the appellate jurisdiction of a higher court a writ ... may issue in aid of the appellate jurisdiction which might otherwise be defeated....’”).29
The Administrative Procedure Act (“APA”) provides additional support for our jurisdiction here. That Act directs agencies to conclude matters presented to them “within a reasonable time,” 5 U.S.C. § 555(b) (1982), and stipulates that the “reviewing court shall ... compel agency action unlawfully withheld or unreasonably delayed ....” 5 U.S.C. § 706(1) (1982). While the APA unquestionably does not confer an independent grant of jurisdiction, [229]*229Califano v. Sanders, 430 U.S. 99, 107, 97 S.Ct. 980, 985, 51 L.Ed.2d 192 (1977), section 706(1) coupled with section 555(b) does indicate a congressional view that agencies should act within reasonable time frames and that court’s designated by statute to review agency actions may play an important role in compelling agency action that has been improperly withheld or unreasonably delayed. See, e.g., Public Citizen Research Group v. Commissioner, Food & Drug Administration (“PCHRG v. FDA”), 740 F.2d 21, 32 (D.C.Cir.1984).
B. The Exclusivity of Our Jurisdiction
We also conclude that our present jurisdiction over claims that affect our future statutory review authority is exclusive.30 It is well settled that even where Congress has not expressly stated that statutory jurisdiction is “exclusive,” as it has here with regard to final FCC actions,31 a statute which vests jurisdiction in a particular court cuts off original jurisdiction in other courts in all cases covered by that statute. Compensation Department of District Five, United Mine Workers v. Marshall, 667 F.2d 336, 340 (3rd Cir.1981); Assure Competitive Transportation, Inc. v. United States, 629 F.2d 467, 471 (7th Cir.1980), cert. denied, 449 U.S. 1124, 101 S.Ct. 941, 67 L.Ed.2d 110 (1981); Rochester v. Bond, 603 F.2d 927, 935 (D.C.Cir.1979); Investment Co. Institute v. Board of Governors of the Federal Reserve System, 551 F.2d 1270, 1278-79 (D.C.Cir.1977). See also Whitney National Bank v. Bank of New Orleans & Trust Co., 379 U.S. 411, 422, 85 S.Ct. 551, 558, 13 L.Ed.2d 386 (1965) (where Congress has enacted a specific statutory scheme of review, the statutory mode must be adhered to notwithstanding the absence of an express statutory command of exclusiveness). By lodging review of agency action in the Court of Appeals, Congress manifested an intent that the appellate court exercise sole jurisdiction over the class of claims covered by the statutory grant of review power. It would be anomalous to hold that this grant of authority only strips the District Court of general federal question jurisdiction under 28 U.S.C. § 1331 (1982) when the Circuit Court has present jurisdiction under a special review statute, but not when the Circuit Court has immediate jurisdiction under the All Writs Act in aid of its future statutory review power.32
The District Court also lacks jurisdiction under both the All Writs Act, 28 U.S.C. 1651(a) and the mandamus statute, 28 U.S.C. § 1361 (1982). The All Writs Act is not an independent grant of jurisdiction to a court; it merely permits a court to issue writs in aid of jurisdiction acquired to grant some other form of relief. See Stern v. South Chester Tube Co., 390 U.S. 606, 608, 88 S.Ct. 1332, 1333, 20 L.Ed.2d 177 (1968); Covington & Cincinnati Bridge Co. v. Hager, 203 U.S. 109, 110, 27 S.Ct. 24, 51 L.Ed. 111 (1906). Because the District Court has no present or future jurisdiction over agency actions assigned by statute to appellate court review, it can contemplate no exercise of jurisdiction that mandamus might aid.33 The mandamus statute, 28 U.S.C. § 1361 also fails to confer jurisdic[230]*230tion on the District Court to compel agency action. Mandamus is an extraordinary remedy that is not available when review by other means is possible. See, e.g., Kerr v. United States District Court, 426 U.S. 394, 403, 96 S.Ct. 2119, 2124, 48 L.Ed.2d 725 (1976); Council of and for the Blind v. Regan, 709 F.2d 1521, 1533 (D.C.Cir.1983); In re Halkin, 598 F.2d 176, 198 (D.C.Cir.1979); Cartier v. Secretary of State, 506 F.2d 191, 199 (D.C.Cir.1974), cert. denied, 421 U.S. 947, 95 S.Ct. 1677, 44 L.Ed.2d 101 (1975). Because review is available in the Court of Appeals under the special review statute and the All Writs Act, action by the District Court under section 1361 is not.
Nor is district court review permissible here under section 703 of the APA, which provides for district court review when statutory review is inadequate.34 Where statutory review is available in the Court of Appeals it will rarely be inadequate. We find untenable any suggestion that appellate review of nonfinal agency action may be inadequate due to Courts of Appeals’ inability to take evidence.35 This precise argument was recently rejected by the Supreme Court in ITT, where the Court held that, if an agency record is insufficient, the Court of Appeals may either remand the record to the agency for further development or appoint a special master under 28 U.S.C. § 2347(b)(3). ITT, 104 S.Ct. at 1940.36
Furthermore, there are compelling policy reasons for holding that the jurisdiction of the Court of Appeals is exclusive. Appellate courts develop an expertise concerning the agencies assigned them for review. Exclusive jurisdiction promotes judicial economy and fairness to the litigants by taking advantage of that expertise. In addition, exclusive jurisdiction eliminates duplicative and potentially conflicting review, Investment Co. Institute, 551 F.2d at 1279, and the delay and expense incidental thereto.
There may be a small category of cases in which the underlying claim is not subject to the jurisdiction of the Court of Appeals (and thus adjudication of the claim in the District Court will not affect any future statutory review authority of the Circuit Court). In such cases, where a denial of review in the District Court will truly foreclose all judicial review, district court review might be predicated on the general federal question jurisdiction statute, 28 U.S.C. § 1331. For example, in Leedom v. Kyne, 358 U.S. 184, 79 S.Ct. 180, 3 L.Ed.2d 210 (1958), the Supreme Court held that, even though there is a statutory prohibition against review of representation orders of the National Labor Relations Board, a District Court has jurisdiction under section 1331 in the very limited circumstance where the Board has clearly violated an express mandate of the statute and the plaintiff has no alternative means of review. See Hartz Mountain Corporation v. Dotson, 727 F.2d 1308, 1311-12 (D.C.Cir.1984). However, we need not tarry over this narrow exception because it is in no way implicated in the case before us. The principal point of this decision is to make clear that where a statute commits review of agency action to the Court of Appeals, any suit seeking relief that might affect the Circuit Court’s future jurisdiction is [231]*231subject to the exclusive review of the Court of Appeals.37
III. Merits of the Unreasonable Delay Claim
As we have noted above, there is no doubt that this court has present jurisdiction to hear claims concerning nonfinal agency action (or inaction) that might affect our future statutory review of final agency action. Nevertheless, given the clear legislative preference for review of final action, we must be circumspect in exercising jurisdiction over interlocutory petitions. Postponing review until relevant agency proceedings have been concluded “permits an administrative agency to develop a factual record, to apply its expertise to that record, and to avoid piecemeal appeals.” Association of National Advertisers v. FTC (“National Advertisers”), 627 F.2d 1151, 1156 (D.C.Cir.1979) (Tamm, J.) (citing McKart v. United States, 395 U.S. 185, 193-94, 89 S.Ct. 1657, 1662-63, 23 L.Ed.2d 194 (1969)), cert. denied, 447 U.S. 921, 100 S.Ct. 3011, 65 L.Ed.2d 1113 (1980). Accordingly, we have found the threshold a litigant must pass to obtain judicial review of ongoing agency proceedings to be a high one. Id.38 As Judge Leventhal emphasized in National Advertisers, “[o]nly in rare instances is a non-final agency action reviewed in the teeth of a general denial of jurisdiction.” 627 F.2d at 1178 (concurring opinion). Thus, we generally will hear only eases of “ ‘clear right’ such as outright violation of a clear statutory provision ... or violation of basic rights established by a structural flaw, and not requiring in any way a consideration of the interrelated aspects of the merits____” Id. at 1180 (emphasis omitted).
Claims of unreasonable agency delay clearly fall into that narrow class of interlocutory appeals from agency action over which we appropriately should exercise our jurisdiction. It is obvious that the benefits of agency expertise and creation of a record will not be realized if the agency never takes action. Agency delay claims also meet Judge Leventhal’s suggested criteria for our interlocutory intervention—not only is there an outright violation of 5 U.S.C. § 555(b)’s mandate that agencies decide matters in a reasonable time, there also is no need for the court to consider the merits of the issue before the agency. Finally and most significantly, Congress has instructed statutory review courts to compel agency action that has been unreasonably delayed. 5 U.S.C. § 706(1).39
In the context of a claim of unreasonable delay, the first stage of judicial inquiry is to consider whether the agency’s delay is so egregious as to warrant mandamus. Although this court has decided several cases involving claims of unreasonable delay, see, e.g., PCHRG v. FDA, 740 F.2d 21 (D.C.Cir.1984); Public Citizen Health Research Group v. Auchter, 702 F.2d 1150 (D.C.Cir.1983); PEPCO, 702 F.2d 1026 [232]*232(D.C.Cir.1983); MCI Telecommunications Corp. v. FCC (“MCI”), 627 F.2d 322 (D.C.Cir.1980); Nader v. FCC, 520 F.2d 182 (D.C.Cir.1975), we have not articulated a single test for when the writ should issue. On reading these cases together, however, one can, discern the hexagonal contours of a standard. Although the standard is hardly ironclad, and sometimes suffers from vagueness, it nevertheless provides useful guidance in assessing claims of agency delay: (1) the time agencies take to make decisions must be governed by a “rule of reason,” PEPCO, 702 F.2d at 1034; MCI, 627 F.2d at 340; (2) where Congress has provided a timetable or other indication of the speed with which it expects the agency to proceed in the enabling statute, that statutory scheme may supply content for this rule of reason, PCHRG v. FDA, 740 F.2d at 34-35; PCHRG v. Auchter, 702 F.2d at 1158, n. 30; PEPCO, 702 F.2d at 1034; (3) delays that might be reasonable in the sphere of economic regulation are less tolerable when human health and welfare are at stake; PCHRG v. FDA, 720 F.2d at 34; PCHRG v. Auchter, 702 F.2d at 1157; see also Blankenship v. Secretary of Health, Education, and Welfare, 587 F.2d 329, 334 (6th Cir.1978); (4) the court should consider the effect of expediting delayed action on agency activities of a higher or competing priority, see, e.g., PCHRG v. FDA, 740 F.2d at 34; PCHRG v. Auchter, 702 F.2d at 1158; (5) the court should also take into account the nature and extent of the interests prejudiced by delay, PCHRG v. FDA, 740 F.2d at 35; and (6) the court need not “find any impropriety lurking behind agency lassitude in order to hold that agency action is ‘unreasonably delayed.’ ” PCHRG v. FDA, 740 F.2d at 34.
Because, in the instant case, the FCC has assured us that it is moving expeditiously on both overcharge claims, we need not test the delay here against the above standard to determine if it is egregious enough to warrant mandamus. But in light of the Commission’s failure to meet its self-declared prior deadlines for these proceedings, we believe these delays are serious enough for us to retain jurisdiction over this case until final agency disposition.
In MCI we announced that:
the entire ratemaking procedure in the 1934 Communications Act revolves around a “rule of reason” ____ It assumes that rates will be finally decided within a reasonable time encompassing months, occasionally a year or two, but not several years or a decade____
Complex regulation must still be credible regulation; the delay at issue here threatens the FCC’s credibility ____ Many of the same considerations that impel judicial protection of the right to a “speedy trial” in criminal cases or implementation of civil decrees with all deliberate speed are not inapposite in agency deliberations. Those situations generally involve protection of constitutional rights, but delay in the resolution of administrative proceedings can also deprive regulated entities, their competitors or the public of rights and economic opportunities without the due process the Constitution requires.
627 F.2d at 340-41 (footnotes omitted).40 In that case we found a four year delay to be unreasonable.41 We observed that unless there was “some limit to the time tariffs unjustified under thfe law can remain in effect ... the regulatory scheme Congress has crafted becomes anarchic and whatever tariff rates the ‘regulated’ entity files become, for all practical purposes, the accepted rates.” Id. at 325. In the instant case, the FCC has delayed almost five [233]*233years on the rate of return inquiry and nearly two years on the proper ratemaking treatment of Western Electric’s CPE development expenses. These delays have permitted- AT & T’s allegedly excessive' returns to “become for all practical purposes, the accepted” ones. Even the agency recognizes, at least with regard to the rate of return delay, that “an unfortunately long time has elapsed since [this] matter first appeared.”42 Whether or not these delays would justify mandamus, we believe they clearly warrant retaining jurisdiction.
IV. Conclusion
In accordance with the foregoing opinion, we order that the court’s mandate shall issue immediately and that within 30 days from the issuance of this decision the FCC shall inform this court of the dates by which the agency anticipates resolution of both refund disputes.43 Every 60 days thereafter, the FCC shall advise the court of its progress in these matters. Prior to final agency orders, any party may petition this court to take additional appropriate action as may be warranted.44