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Md-11 flight crew reported anti icing systems failure resulting in loss of flight directors and autopilot functionality during approach.

Narrative:

Received wshld heat left fail when placed all a/I (anti-icing) on before entering crosswind. On the arrival descending to FL200 in heavy rain and moderate or greater turbulence; ats off illuminated and ATC requested right orbit at present position for spacing. Shortly thereafter received IAS on both pfds (primary flight display); ap (autopilot) off; then sel elev feel man; and sel flap lmt ovrd. Lost both flight directors; and neither ap would remain engaged; with all malfunction indications coming on and going off intermittently.while attempting to maintain aircraft control and talk to arrival; experienced deviations to clearance. Radios were very congested due to multiple deviation requests. Advised ATC as soon as possible of flight systems malfunction and requested heading. Was about to request a block altitude for troubleshooting when ATC asked if we wanted priority handling which we accepted. We suspected icing was our issue; and this allowed us immediate descent to lower/warmer altitude while the first officer (first officer) ran checklists. The suspect systems remained intermittent remainder of flight which required a manually flown raw data ILS to an uneventful landing in heavy rain. All systems returned to normal by rollout.severe weather; system malfunction; heavy radio frequency congestion. Hard to say because the multitude of weather related issues were difficult to predict; but the pitot static anti-ice systems appear to have not been sufficient for the conditions.

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Original NASA ASRS Text

Title: MD-11 flight crew reported Anti Icing systems failure resulting in loss of flight directors and Autopilot functionality during approach.

Narrative: Received WSHLD HEAT L FAIL when placed all A/I (Anti-Icing) on before entering crosswind. On the arrival descending to FL200 in heavy rain and moderate or greater turbulence; ATS OFF illuminated and ATC requested right orbit at present position for spacing. Shortly thereafter received IAS on both PFDs (Primary Flight Display); AP (Autopilot) OFF; then SEL ELEV FEEL MAN; and SEL FLAP LMT OVRD. Lost both flight directors; and neither AP would remain engaged; with all malfunction indications coming on and going off intermittently.While attempting to maintain aircraft control and talk to arrival; experienced deviations to clearance. Radios were very congested due to multiple deviation requests. Advised ATC as soon as possible of flight systems malfunction and requested heading. Was about to request a block altitude for troubleshooting when ATC asked if we wanted priority handling which we accepted. We suspected icing was our issue; and this allowed us immediate descent to lower/warmer altitude while the FO (First Officer) ran checklists. The suspect systems remained intermittent remainder of flight which required a manually flown raw data ILS to an uneventful landing in heavy rain. All systems returned to normal by rollout.Severe weather; system malfunction; heavy radio frequency congestion. Hard to say because the multitude of weather related issues were difficult to predict; but the pitot static anti-ice systems appear to have not been sufficient for the conditions.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.