Was it contractual estoppel or estoppel by misrepresentation? The former, in Olympic Airways SA (In special liquidation) v ACG Acquisition XX LLC,  EWCA Civ 369. Olympic Airways (now bust) leased a 17-year-old plane from ACG which had previously been leased to Air Asia. On taking delivery of the plane in 2008, Olympic signed a certificate of acceptance stating that the plane was in acceptable shape, subject to any listed discrepancies. The plane was not in good shape, in fact; unbeknownst to either ACG or Olympic until a pre-flight inspection, it was not in a safe or airworthy condition. AGC claimed rent and maintenance reserves from the time of delivery until November 2010; Olympic counterclaimed for breach of contract for failure to deliver the plane in 'contractual condition'. ACG argued that the deal was that the certificate of acceptance was conclusive proof that the aircraft was in acceptable condition at the time of delivery (contractual estoppel) or that the certificate gave rise to an estoppel by representation on the part of Olympic, which ACG relied on to its detriment in taking the plane off Air Asia's hands for redelivery to Olympic.
ACG was successful at trial, the judge rejecting the theory of contractual estoppel but accepting that with respect to estoppel by misrepresentation. Olympic's counterclaim failed. On appeal, the Court of Appeal said right result, but wrong form of estoppel. Olympic had, in signing the certificate of acceptance, accepted the risk that the plane might not be in the required condition. It was bound by that acknowledgment and couldn't then say there had been breach of the underlying contract. Tomlinson LJ emphasised the commercial realities of aircraft leasing, in which lessors are involved in the financing but not the operation or maintenance of planes -- and in which lessees understand that they may have to accept delivery without being absolutely certain of a plane's actual condition. Olympic knew reconditioning work would have been carried out at the previous lessee's instruction and had opportunities for inspection before delivery. As a result, it wasn't necessary to consider whether either party had made misrepresentations to the other.