Lewis Hamilton's hopes of a record-breaking eighth F1 title hang in the balance as the São Paulo Grand Prix stewards have disqualified the Mercedes driver from qualifying.
After Hamilton dominated the session to set the fastest lap by almost half-a-second, FIA technical delegate Jo Bauer discovered the DRS, once opened, was more than the permitted 85mm as prescribed by the regulations.
A stewards' investigation was adjourned overnight as new evidence was required on Saturday that could not be provided post-qualifying.
The stewards ultimately determined Mercedes had breached article 3.6.3 of the sport's technical regulations that deemed the rear wing illegal, leading to Hamilton's qualifying time being deleted.
The decision means Hamilton will start the final sprint event of the year from the back of the grid at Interlagos.
Hamilton is now faced with an uphill task to score significant points this weekend, with a charge to the top 10 in 24 laps unlikely before a five-place grid penalty is incurred for the grand prix following an internal combustion engine change.
A lengthy stewards' verdict confirmed Bauer was able to pass through its gauge to check the DRS opening "at the outer section of the wing".
It added: "This test was repeated four times with two different gauges, once being done in the presence of the stewards and representatives of the competitor."
Following an overnight adjournment, with the hearing resumed on Saturday morning, the stewards stated that "the competitor asserted that the design is intended to meet the regulations.
"It was clear to the stewards that the additional deflection was due to additional play either in the DRS actuator or the pivots at the end, or some combination or other fault with the mechanism, or incorrect assembly of the parts.
"The stewards heard, from both the team and the FIA that the same design has been tested many times during the season and uniformly passed.
"Further, the FIA has examined the design of the area of the car in question and are satisfied that the design meets the intent of the regulation.
"There is, therefore, no question in the minds of the stewards that the test failure indicates any intent to exceed the maximum dimension either by action or
"The competitor also noted, that Art 3.6.3 of the regulation states a maximum
dimension, which is possible to measure without applying a force or load
"It is not until a force is applied, that the gauge is able to go through. There was no disagreement that the test itself was undertaken as described."
A discussion then ensued over the intricacies of the technical directive upon which the tests are carried out, with the stewards satisfied "the test that was carried out was in conformity with the TD and its legitimate aims"
Mercedes also tried to argue that it passed the test when the gauge was applied to the middle sector of the wing, further underlining the fact there was no intent to breach the regulations.
The stewards countered that while the "point may be true...which sections failed is not relevant to the fact that the wing did fail the test".
The report added: "The competitor noted that this is not a systemic breach, and is indeed unique. It was, rather, something gone wrong.
"The competitor further noted that they would have liked to have had the opportunity to inspect the parts with a view to having some explanation for the stewards as to how the problem arose.
"However, the stewards fundamentally accept the competitor’s explanation that the cause of the failed test was something “gone wrong” rather than a deliberate action."
Mercedes further suggested it is a regular practice for the FIA Technical Department to allow teams to fix minor problems they find with their cars, even during parc fermé conditions of qualifying.
The team added that had the problem been recognised during qualifying it would have "sought and...received permission to fix the parts or tighten bolts if needed"
The stewards replied they were "sympathetic to this argument and analysed whether they felt this was a mitigating circumstance.
"It is often a mitigating circumstance to make allowances for crash damage. However, the stewards could not extend this argument to cover parts that were found out of conformity in post-session checks with no obvious reason in evidence other than considering normal running at this event.
"In the end, the regulations are clear and at the moment of the conformity check, the car did not comply."
The stewards also noted video evidence of Red Bull's Max Verstappen inspecting and touching the rear wing of Hamilton's car during parc fermé.
The stewards' report added: "In summary, the competitor of car 44 also agreed that it was unlikely that Verstappen’s actions caused the fault, however they felt that it was an open question.
"The stewards, however, were fully satisfied, having extensively reviewed the totality
of the evidence regarding that incident, that it has no bearing on this case."
Overall, "the stewards agree with the competitor that this is something gone wrong, rather than an intentional act or design but did not find there to be mitigating circumstances."
In addition, article 1.3.3 of the International Sporting Code states that “it shall be no defence to claim that no performance advantage was obtained”.
In conclusion "the stewards order the usual penalty for technical non-compliance of disqualification from the qualifying session."
Mercedes has been reminded of its right to appeal.