{"id":"F2006B09861","name":"AD/F50/34 - Electrical Power - AC Emergency Inverter","slug":"ad-f50-34-electrical-power-ac-emergency-inverter","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54950,"registerId":"commonwealth-F2006B09861-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/34 - Electrical Power - AC Emergency Inverter","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)  \nFokker F50 (F27 Mk 50) Series Aeroplanes\n\nAD/F50/34 Electrical Power \\- AC Emergency Inverter 4/90\n\nApplicability: All F27 Mk50 aircraft S/Nos 20103 to 20161 inclusive. Requirement: Action in accordance with Fokker SB F50-24-009 or later revision.\n\nNote: RLD Airworthiness Directive BLA 90-003 also refers.\n\nCompliance: Prior to 19 January 1991.\n\nBackground: When the AC Power is switched from NORMAL to EMERGENCY, the attitude and heading reference system (AHRS) does not work for approximately 45 seconds, due to a combination of tolerances built into the emergency inverter and the AHRS. This Airworthiness Directive calls for a wiring change to the circuit of the emergency inverter. The emergency inverter will now be switched ON from the standby mode. This will make sure that the AHRS does not become inoperative when the AC power is switched from normal to emergency.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific technical fault in a specific aircraft type. It has not expanded beyond its original purpose."},"complexity_factors":["Single, specific technical requirement (wiring change per manufacturer service bulletin)","Narrow applicability (59 specific aircraft by serial number)","No defined terms section or interpretive provisions","No conditional logic or nested exceptions","Straightforward compliance deadline with no alternative methods","Cross-reference to only one related directive (RLD BLA 90-003) and one manufacturer document (Fokker SB F50-24-009)"],"plain_english_summary":"This is an **Airworthiness Directive** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nOrders a wiring modification to the emergency electrical system on certain Fokker F50 aeroplanes.\n\n**The safety problem:**\nWhen pilots switch from normal to emergency AC power, the aircraft's attitude and heading reference system (AHRS) — the equipment that tells the pilots which way the plane is pointing and how it's oriented — stops working for about 45 seconds. This happens because of timing mismatches between the emergency inverter (a device that converts DC battery power to AC power) and the AHRS system.\n\n**The fix:**\nRewire the emergency inverter so it switches on from standby mode rather than starting from cold. This keeps the AHRS powered continuously during the transition, eliminating the 45-second blackout.\n\n**Who it affects:**\nOwners and operators of Fokker F50 aircraft with serial numbers 20103 through 20161 — 59 specific aircraft.\n\n**Why it matters:**\nA 45-second loss of attitude and heading information during an emergency is dangerous. Pilots could become disoriented, especially in poor weather or at night, potentially leading to loss of control. This directive prevents that safety gap.\n\n**Compliance deadline:**\nBefore 19 January 1991 (now long past — this is a historical directive)."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive’s scope is confined to F27 Mk50 aircraft with serial numbers 20103–20161 and mandates a wiring change per Fokker SB F50-24-009 (or later revision) to prevent temporary AHRS inoperative time when AC power is switched. The source contains no indication that the scope was altered from the directive’s original stated purpose (Applicability; Requirement; Background)."},"complexity_factors":["Narrow applicability limited to specific serial-number range (Applicability).","Single, well-defined technical remedy (wiring change) called for by a manufacturer service bulletin (Requirement; Background).","Mandatory compliance by a fixed date creates a clear operational deadline (Compliance).","Acceptance of 'or later revision' of the service bulletin introduces minor regulatory flexibility (Requirement).","Reference to another related airworthiness directive adds a cross-reference for implementers (Note)."],"plain_english_summary":"Requires a wiring modification to the AC emergency inverter so it switches on from standby when selected, preventing about a 45‑second AHRS outage when AC power changes to emergency.  \n\nApplies to Fokker F50 (F27 Mk 50) serials 20103–20161; operators/owners must complete the change per Fokker SB F50‑24‑009 (or later revision) by 19 January 1991, at their expense."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-34-electrical-power-ac-emergency-inverter","history":"/api/acts/ad-f50-34-electrical-power-ac-emergency-inverter/history","analysis":"/api/acts/ad-f50-34-electrical-power-ac-emergency-inverter/analysis","conflicts":"/api/acts/ad-f50-34-electrical-power-ac-emergency-inverter/conflicts","importantCases":"/api/acts/ad-f50-34-electrical-power-ac-emergency-inverter/important-cases","documents":"/api/acts/ad-f50-34-electrical-power-ac-emergency-inverter/documents"}}