In the event of a Mode IB abort during an Apollo launch (an abort initiated between 3 and 30.5 km altitude), a pair of canards would be deployed from the tip of the spacecraft's LES in order to force the command module to weathervane blunt-end forward, because the CM's parachutes (stored at the apex of said module) were only designed to deploy downwind (with the CM's apex pointing backwards, and its blunt end facing forward).1

However, on 19 May 1965, during the A-003 abort test, the Little Joe II booster propelling the spacecraft suffered an almost immediate loss of control,2 and started to inexorably roll faster and faster until the launch vehicle disintegrated. This automatically triggered an abort, and the canards deployed, but, as the capsule was still rolling rapidly (at a rate of approximately 260 degrees per second, according to Wikipedia), they failed to flip the CM tail-first. As a result, the parachutes deployed into the wind... and worked perfectly, despite the nose-first attitude and extremely high roll rate.

Why weren't the LES canards deleted (which would have made the LES, and, thus, the vehicle as a whole, somewhat lighter), despite their having been proved unnecessary (as the parachutes turned out to be perfectly cool with deploying with the CM nose-first)?

1: For a pad abort, or a Mode IA abort (between launch and 3 km altitude), the canards would still deploy, but the job of flipping the CM ass-first would be performed mainly by the LES's pitch motor; for a Mode IC abort (between 30.5 km altitude and LES jettison at ~90 km altitude), the canards wouldn't have enough control authority to flip the CM (because thin air), and the CM's RCS thrusters would turn the trick (and the CM) instead.

2: This was due to an error in assembly of the booster, where the cables to the Little Joe II's pitch and roll actuators were inadvertently transposed; thus, a pitch command would instead cause the booster to roll, and vice versa.

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    $\begingroup$ Just guessing, but as parachute deployment is a fairly chaotic process, the fact that the parachutes deployed correctly on that one occasion probably wasn't taken to mean that they'd deploy correctly in all possible scenarios. $\endgroup$ – Russell Borogove Jun 30 '19 at 1:15

Because a massive Saturn V (or even a Saturn IB) can't tumble 260 °/s like a Little Joe can. Even if it could, the abort system is triggered at 20 °/s:

Within 2.5 seconds after lift-off, a launch vehicle malfunction caused the vehicle to go out of control. The resulting roll rate caused the launch vehicle to break up before second-stage ignition, and a low-altitude spacecraft abort was initiated instead of the planned high-altitude abort. The launch escape system canard surfaces deployed and survived the severe environment. The high roll rates (approximately 260° per second at the time of canard deployment) induced by the launch vehicle malfunction stabilized the launch escape vehicle in a tower-forward attitude, which overcame the destabilizing effect of the canards. Postflight simulations verified the ineffectiveness of the canards at the high roll rate, but showed that the canards would be effective at the 20° per second roll rate limit of the Saturn emergency detection system.

Apollo Program Summary Report, section 2.2.4.

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  • $\begingroup$ Unless the extremely high roll rate was necessary in order for the CM's parachutes to deploy with the CM flying nose-first, this doesn't answer the question. (Also, the A-003 Little Joe II was rolling at approximately 335°/sec when it broke up; the 260°/sec figure is for the CM/LES combination at the time the canards deployed, by which time the capsule's roll rate had already slowed down considerably.) $\endgroup$ – Sean Jul 3 '19 at 23:07
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    $\begingroup$ The point is that A-003 is not a good test of whether the canards are necessary. Too many details are different from an actual Saturn flight. The postflight simulations cited in the answer and other test flights confirmed the effectiveness of the canards, and the decision was made to retain them rather than gamble on the parachutes. $\endgroup$ – DrSheldon Jul 4 '19 at 2:20
  • $\begingroup$ Exactly. The situation was considerably worse than even the worst-case scenario for a Saturn flight - and yet the parachutes still deployed normally. $\endgroup$ – Sean Jul 4 '19 at 2:37

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