58 passengers per flight. With officials acutely aware of the aircraft's poor reliability and fearful of possible crashes, Soviet decision-makers deliberately limited flight frequency to the minimum allowing them to claim regular service, and also limited passenger load to minimize the impact and political fallout of a possible crash. Airframe test failures A serious problem was discovered when two Tu-144S airframes suffered structural failures during laboratory testing just prior to the Tu-144 entering passenger service. Details are included in a chapter in Fridlyander's memoirs and mentioned by Bliznyuk et al. The problem, discovered in 1976, may have been known prior to this testing; a large crack was discovered in the airframe of the prototype Tu-144 (aircraft 68001) during a stopover in Warsaw following its appearance at the 1971 Paris Air Show. The aircraft was assembled from parts machined from large blocks and panels, many over long and wide. While at the time, this approach was heralded as an advanced feature of the design, it turned out that large whole-moulded and machined parts contained defects in the alloy's structure that caused cracking at stress levels below that which the part was expected to withstand. Once a crack started to develop, it spread quickly over many metres, with no crack-arresting design feature to stop it. In 1976, during repeat-load and static testing at TsAGI (Russia's Central Aerohydrodynamic Institute), a Tu-144S airframe cracked at 70% of expected flight stress with cracks running many metres in both directions from their origin. Later the same year, a test airframe was subjected to a test simulating the temperatures and pressures occurring during a flight. The Tu-144 was placed in a hyperbaric chamber and heated to . Contraction and expansion happened because of the cooling during ascent and descent, heating during supersonic acceleration and cruise and because of the pressure change from high altitude (low outside pressure causing the airframe to expand) to ground-level pressure (causing it to contract). The airframe cracked in a similar way to that of the TsAGI load testing. While fatigue cracks of an acceptable length are normal in aircraft, they are usually found during routine inspections or stopped at a crack-arresting feature. Aircraft fly with acceptable cracks until they are repaired. The Tu-144 design was the opposite of standard practice, allowing a higher incidence of defects in the alloy structure, leading to crack formation and propagation many metres in length. Decision to