SAE ARP 6385-2017 Aircraft Fuel Pump Mechanical and Electrical Safety Design.pdf

1、 _ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising ther

2、efrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2017 SAE International All rights reserved. No part of this

3、publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-49

4、70 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/standards.sae.org/ARP6385 AEROSPACE RECOMMENDED PRACTICE ARP6385 Issued 2017-10 Aircraft Fuel Pump Mechanical an

5、d Electrical Safety Design RATIONALE This document is a continuation of the safety information presented in ARP594, which covered the thermal aspects of fuel pump safety design. Other failure modes in FAA AC 25.981-1C fall under the umbrellas of mechanical and electrical design. This new document wi

6、ll address these key elements and when used in combination with ARP594 and ARP5794, will represent a basis for the proper pump design and testing, and support certification of an airframe fuel pump installation. 1. SCOPE The requirements presented in this document address the key considerations for

7、mechanical and electrical safety in aircraft fuel pump design. Document sections focus on understanding safety relative to an electrically motor driven fuel pump assembly acting as an ignition source for explosive fuel vapors within the airplane tank. 1.1 Purpose This Aerospace Recommended Practice

8、(ARP) provides fuel booster pump design considerations commensurate with industry requirements for prevention of ignition of explosive fuel vapors and the confinement of spark-initiated explosions by means of mechanical and electrical design features. Guidelines are presented for proper design of fu

9、el pumps and systems to meet the intent of 14CFR 25.901(c), Amendment 25-40 or later, and 14CFR 25.981, Amendment 25-102 or later and FAA AC 25.981-1C for in-tank ignition sources and the general safety requirements of MIL-STD-882. In addition, recommendations are presented for proper assembly, test

10、ing, and repair/overhaul to verify safe fuel pump design that prevents mechanical and electrical arcs and sparks. 2. APPLICABLE DOCUMENTS The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of

11、other publications shall be the issue negotiated between Seller and Buyer. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supercedes applicable laws and regulations unless a specif

12、ic exemption has been obtained. 2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. ARP594 Fuel Pump Thermal Safety Design ARP4761 Guidelines and Methods for

13、 Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment SAE INTERNATIONAL ARP6385 Page 2 of 12 ARP5794 Centrifugal Aircraft Fuel Pump Requirements, Design and Testing, Aerospace Standard ARP8615 General Specification For Fuel System Components 2.2 Military Publications Copi

14、es of these documents are available online at http:/quicksearch.dla.mil. MIL-STD-810 Environmental Engineering Considerations and Laboratory Tests MIL-STD-882 System Safety 2.3 Other Federal Aviation Administration Advisory Circular Fuel Tank Ignition Source Prevention Guidelines, Document Number AC

15、 25.981-1C. Title 14, Code of Federal Regulations Aeronautics and Space, Paragraph 25.981, Fuel Tank Ignition Prevention RTCA DO160, Environmental Conditions and Test Procedures for Airborne Equipment ASTM E659 Standard Test Method for Autoignition Temperature of Chemicals 3. RELATED REQUIREMENTS FR

16、OM 14CFR 25.981, FAA AC 25.981-1C, AND MIL-STD-882 3.1 Introduction For commercial fuel pumps, the governing regulations for fuel tank safety are provided in 14CFR 25.981 Amendment 125. Detailed guidance to demonstrate compliance for fuel tank ignition prevention is provided in FAA AC 25.981-1C. The

17、re are four primary phenomena that can result in ignition of fuel vapors within an airplane fuel tank. These categories are as follows: Electrical Arcs and Sparks Filament Heating Friction Sparks Hot Surface Ignition or Auto-ignition For military applications, safety guidance is provided by MIL-STD-

18、882, which does not delineate failure categories but focuses on the System Safety Process of identifying, assessing, documenting, and reducing safety risks. The risks are categorized by severity and probability and ranked in a Risk Assessment Matrix. The focus is on risk reduction through design imp

19、rovements, warning devices, signage, procedures, training, and personal protective equipment. In addition to the criteria set forth in MIL-STD-882, the design guidelines presented in FAA AC 25.981-1C should be considered for military products to provide the safest product. 3.2 Definitions ARC FAULT

20、CIRCUIT BREAKER: A device that provides circuit breaker protection by detecting electrical arcing faults and interrupts electrical power to the circuit. AUTO-IGNITION TEMPERATURE: The minimum temperature at which an optimized flammable vapor and air mixture will spontaneously ignite when heated to a

21、 uniform temperature in a normal atmosphere without an external source of ignition. Refer to ASTM E659 for information on standard autoignition test procedures. SAE INTERNATIONAL ARP6385 Page 3 of 12 CRITICAL DESIGN CONFIGURATION CONTROL LIMITATIONS: A type of Airworthiness limitations that define t

22、hose features of the design that must be maintained to ensure that ignition sources will not develop within the fuel tank. These parameters must be verified prior to initial installation in the aircraft and also during maintenance and overhaul as determined by the Component Maintenance Manual. (Othe

23、r types of fuel tank system Airworthiness limitations may include mandatory replacement times, inspection intervals, and related inspection procedures.) ELECTRICAL ARCS: Electrical arcs occur between electrodes which are in contact with each other and carry excessive current which results in melting

24、 at the contact points. This may result in electric arc plasma and/or ejection of molten or burning material. The term thermal sparks is used interchangeably with electrical arcs. ELECTRICAL SPARKS: A spark that is initiated by a potential difference which causes an electrical breakdown of a dielect

25、ric, such as a fuel/air mixture, produced between electrodes which are initially separated, with the circuit initially carrying no current. The term voltage sparks can be used interchangeably with electric sparks. ELECTRO-STATIC DISCHARGE: ESD is the sudden flow of electricity between two electrical

26、ly charged objects caused by contact, an electrical short, or dielectric breakdown. EXPLOSION PROOF: Components designed and constructed such that an internal arc/spark or explosion is contained and will not ignite flammable vapors or liquids surrounding the component under any normal or abnormal op

27、erating condition. FILAMENT HEATING: Filament heating occurs when current is passed through a metallic material. Testing has shown that a small level of current when passed through steel wool will ignite a flammable mixture. FRICTION SPARKS: A heat source in the form of a spark that is created by me

28、chanical contact, such as trapped metallic debris contacting with rotating components. GROUND FAULT INTERRUPTER: A device that provides circuit breaker protection by detecting an electrical current leak to ground condition and interrupting the electrical supply. HOT SHORT: Electrical energy introduc

29、ed into equipment or systems as a result of unintended contact with a power source of a different type or voltage, i.e., 115 VAC applied to 28 VAC equipment. Causes could be incorrect installation or damaged insulation on adjacent wires. HOT SURFACE IGNITION: The initiation of a flame due to a fuel/

30、air mixture coming in contact with a surface which exceeds the fuels auto ignition temperature. The Hot Surface Ignition Temperature (HSIT) is dependent on many factors including surface geometry, ambient pressure, air flow, how the fuel comes in contact with the surface, as well as fuel and air tem

31、perature. IGNITION SOURCE: A source of sufficient energy to initiate combustion of a fuel/air mixture. Surfaces that exceed the auto-ignition temperaure of the flammable vapor under consideration are ignition sources. MAXIMUM ALLOWABLE SURFACE TEMPERATURE: A surface temperature within the fuel tank

32、that provides a safe margin under all normal and failure conditions, which is at least a delta of 50 F (27.8 C) below the lowest expected auto-ignition temperature of the approved fuels. For example, the auto-ignition temperature for kerosene based fuels under static sea level conditions is 450 F (2

33、32.2 C). This results in a maximum allowable surface temperature of 400 F (204.4 C) for an unaffected component surface. 3.3 Relevant Fuel Pump Failure Modes Table 1 provides a list of potential failure modes applicable to fuel pumps as related to in-tank ignition safety. SAE INTERNATIONAL ARP6385 P

34、age 4 of 12 Table 1 - Fuel pump failure modes related to safety compliance Failure Category Description of Design Issue or Failure Mode Friction sparks (NOTE: Impeller reference includes main hydraulic impeller as well as secondary impellers used in liquid rings) Ingestion of pump inlet components i

35、nto the pump impeller releasing debris into the fuel tank. Pump inlet housing degradation, allowing the pump inlet check valve to contact the impeller. Premature failure of fuel pump radial or thrust bearings allowing unintentional contact between rotating and stationary parts if these parts are mad

36、e of sparking material. Use of metal impellers (i.e., steel or other sparking metals) that may produce friction sparks if debris enters the pump. Debris lodged inside pumps. Electrical arcs and sparks Failure of one or more phases of the stator winding during operation of the fuel pump motor resulti

37、ng in arcing phase to phase or arcing through the pump housing. Arcing due to the exposure of electrical connections within the pump housing that have been designed with inadequate clearance to the pump cover. Pump power supply connectors have corroded resulting in fuel leakage and elecrical arcing.

38、 Electrical connections within the pump housing have been designed with inadequate insulation from the metallic pump housing, resulting in arcing. Internal wires coming in contact with the pump rotating group, energizing the rotor and arcing at the impeller/adapter interface. Loss or degredation of

39、bonding across component interfaces due to wear or corrosion. Insufficient ground fault current protection capability. Loss or degredation of bonding of pump components to structure. Electrical arcing at connections within electrical connectors due to bent pins or worn contacts. Fuel leakage and sub

40、sequent fuel fire outside of the fuel tank caused by corrosion of electrical connectors inside the pump motor which led to electrical arcing through the connector housing (connector located outside the fuel tank). Selection of improper insulating materials in connector causing degradation of the mat

41、erial because of contact with fuel that is used to cool and lubricate the pump motor. Wear of teflon sleeving and wiring insulation on wires in metallic conduits located inside fuel tanks, allowing arcing from wire through the conduits into fuel tank ullages. Damage to insulation on wiring routed ad

42、jacent to the fuel tank exterior surfaces that resulted in arcing to the metallic fuel tank surface. Hot surface ignition or auto-ignition Omission of cooling port tubes between the pump and the motor assemblies during pump overhaul. Extended dry running of fuel pumps in empty fuel tanks, which was

43、contrary to the manufacturers recommended procedures. Thermal switches aging over time resulting in a higher trip temperaure. Locked rotor or dragging rotor condition caused by debris, damaged or deformed inlet screens, or incorrect mechanical clearances. Filament Heating Electrically conductive FOD

44、 or contamination causing heat generation between pins of an electrical connector. Poor bonding of internal components to structure. SAE INTERNATIONAL ARP6385 Page 5 of 12 3.4 Required Safety Inspections In order to verify the integrity of the key features of the pump design, all safety related feat

45、ures and dimensions of the design (from the assembly level down to the individual components) will be designated as CDCCL (Critical Design Configuration Control Limitation) on their respective drawings. A CDCCL can be a visual feature (such as the presence of insulative parts), a single component le

46、vel dimensional feature, or an assembly dimensional feature. The CDCCL verification can also be part of the assembly procedure, i.e., if a design feature is missing, it will prevent the pump from being fully assembled. Each of these characteristics will be verified by some type of inspection and a p

47、ermanent record made of conformance. The same inspection verification applies to CDCCL dimensions on affected components that are being overhauled or repaired. Verification of the repair or overhaul plan with the Buyer and Certification Agency is recommended. After initial certification, any changes

48、 in CDCCL requirements must be approved by the Buyer and Certification Agency. 3.5 Safety Assessment Methodology Compliance with 14CFR 25.981 requires a failure analysis for the fuel tank installation to substantiate that ignition sources will not be present in the fuel tanks. An assessment of the f

49、uel pump ignition sources will be used to support that analysis. AC 25.981-1C, paragraph 10 Safety Analysis provides guidance for conducting such an analysis.Designing to a Dual Fault Tolerant methodology is the recommended (but not required) approach to meeting the safety criteria in 14CFR 25.901(c), Amendment 25-40 or later, and 14CFR 25.981, Amendment 25-102 or later and FAA AC 25.981-1C. Dual Fault Tolerant i