{"id":"F2006B02938","name":"AD/B737/39 - APU Fire Detector Element","slug":"ad-b737-39-apu-fire-detector-element","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42280,"registerId":"commonwealth-F2006B02938-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/39 - APU Fire Detector Element","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBoeing 737 Series Aeroplanes\n\nAD/B737/39 APU Fire Detector Element 7/90\n\nApplicability: All model 737 series aircraft equipped with Walter Kidde APU fire detection systems.\n\nRequirement: Inspect to ensure a Walter Kidde fire detector element is installed in the APU compartment. This inspection may be performed by viewing through the APU cooling air exhaust outlet. The Walter Kidde element is protected by a perforated shield surrounding the length of the element. If the perforated shield is not seen, open the lower APU shroud and verify that for 737-300 and 737-400 series aircraft, the fire detector element installed is Boeing P/N 10-61096-316 / Walter Kidde P/N 894481, and for 737-100 and 737-200 series aircraft, the fire detector element installed is Boeing P/N 10-62061-6 or P/N 10-61096-116.\n\nCompliance: Prior to 19 July 1990.\n\nBackground: Boeing has advised that several aircraft with Walter Kidde APU fire detection systems were found to have a Systron-Donner fire detector element fitted instead of the correct Walter Kidde element. This would result in a positive flight deck fire detector test even though the system would not have detected an actual fire.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific technical defect in a specific aircraft system. It has not expanded beyond its original purpose of ensuring correct fire detector installation in Boeing 737 APUs."},"complexity_factors":["Single, specific technical requirement with clear inspection method","Only 4 part numbers to verify across 4 aircraft variants","No cross-references to other legislation or regulations beyond the enabling Civil Aviation Regulations 1998","Simple conditional logic: if shield not visible → open shroud → verify part number","Single compliance deadline with no exceptions or alternative methods","Short document (approximately 200 words) with minimal defined terms"],"plain_english_summary":"This CASA Airworthiness Directive orders operators of Boeing 737-100/200/300/400 series to inspect APU fire detectors because some aircraft have incorrect Systron‑Donner units that pass cockpit tests but would fail to detect a real fire. It requires verifying the correct Walter Kidde detector is installed to prevent undetected APU fires — a direct safety risk to aircraft and occupants."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"Scope has not changed from the instrument's apparent original intent: it targets verification and correction of APU fire detector elements on Walter Kidde‑equipped Boeing 737s by inspection and part‑number confirmation, limited to the identified models and parts."},"complexity_factors":["Narrow applicability (low complexity): applies only to Boeing 737 series aircraft equipped with Walter Kidde APU fire detection systems (Applicability).","Simple compliance action: a visual inspection through the APU cooling air exhaust outlet or opening the lower APU shroud to verify presence of a perforated shield (Requirement).","Part-number verification requirement increases precision but not complexity: different approved P/Ns specified by aircraft series (Requirement).","Fixed, near-term deadline creates operational urgency but not technical difficulty: compliance prior to 19 July 1990 (Compliance).","Clear safety rationale but limited scope: wrong element (Systron‑Donner) may produce a false-positive test yet fail to detect real fire (Background).","Implementation discretion: allowance to inspect by viewing through the exhaust outlet introduces room for variable judgment about sufficiency of visual confirmation (Requirement).","Compliance burden: minor maintenance labour and potential short downtime if shroud must be opened and parts replaced (Requirement).","Decision authority noted: directive issued under Civil Aviation Safety Authority/Part 39 framework, so CASA enforces the requirement (header)."],"plain_english_summary":"This Airworthiness Directive requires operators of Boeing 737s fitted with Walter Kidde APU fire-detection systems to inspect the APU compartment and confirm the correct Walter Kidde detector element (identified by a perforated shield or specific part numbers) is installed; if not visible, the lower APU shroud must be opened for verification. It affects aircraft operators and maintenance organisations and matters because an incorrect Systron‑Donner element can give a cockpit test pass while failing to detect an actual APU fire. Compliance was required by 19 July 1990."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-39-apu-fire-detector-element","history":"/api/acts/ad-b737-39-apu-fire-detector-element/history","analysis":"/api/acts/ad-b737-39-apu-fire-detector-element/analysis","conflicts":"/api/acts/ad-b737-39-apu-fire-detector-element/conflicts","importantCases":"/api/acts/ad-b737-39-apu-fire-detector-element/important-cases","documents":"/api/acts/ad-b737-39-apu-fire-detector-element/documents"}}