<h1>Airlines challenge tariff recalculation expanding hypothetical regulatory asset base, question status of internal government letter and remand limits</h1> An airline industry association has approached the Supreme Court challenging a 1 July order of the Telecom Disputes Settlement and Appellate Tribunal regarding principles for determining aeronautical tariffs for major airport operators. The association alleges the tribunal exceeded the limited remand granted by the Supreme Court, unlawfully reopening settled issues on computation of the Hypothetical Regulatory Asset Base (HRAB) earlier affirmed in a 2022 judgment. It contends the tribunal improperly treated an internal government letter as a binding directive, inflated HRAB from Rs 966 crore to Rs 4,848 crore, and thereby enabled an unwarranted financial windfall for airport operators. The appeal raises questions on remand limits, the status of internal correspondence, deference to regulatory expertise, and tariff finality, with potential implications for airport charges and passenger fares.