# AC 20-34D: Prevention of Retractable Landing Gear Failures - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Historical - Approved: August 8, 1980 - Family: AC 20-34 - Pages: 4 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/777228C04DE00D0A862569C3004BA5C4.0001 - Page: https://openairdocs.org/ac/20-34 ## Versions - AC 20-34D (Historical), approved Aug 8, 1980 ## Text ### Page 1 ADVISORY kc 20034D DATE 8/8/80 CIRCULAR DEPARTMEST OF TR,4XSPORTATIOS Federal Aviation Administration Washington, D.C. Subject : PREVENTION OF RETRACTABLE IANDING GEAR FAIWES 1. PURPOSE. This advisory circular updates statistical information related to landing accidents involving aircraft with retractable landing gear and suggests procedures to minimize those accidents. 2 CANCELLATION. Advisory Circular 20.34C, Prevmtion of Retractable &ding Gear Failures, dated May 17, 1979, is canceled. 3 DISCUSSION. A review of the Federal /Mation Administration's &era1 Aviation Accident Factual Reports for the year 1?79 disclosed that 1,002 airplanes quipped with retractable landing gear were involved in accidents. Of those 1,002 airplanes, 106 or 10.5 percent were involved in "landing gear" accidents. Further study shmed that 63 percent of the 106 accidents FiFeTe the result of a human factor and 37 percent involved m&anical/technical reasons. Accidents involving retractable landing gear can be reduced with deliberate, careful, and - continued use of the checklist by pilots, and the performance of maintenance, as recommnded by the aircraft manufacturer, by qualified personnel. 4. OPERATIo1\7sILi FACTOPS AND PEXCEWIAGES INVOLVED IN RETEWCMBLE GEAR AIRCRAFT ACCIDENTS. a. Neglected to extend landing gear -- 35.8 percent. b 0 Inadvertent retraction of land- gear -- 10.3 percent. c. Activated gear, but failed m check gear psition -- 11.3 percent do Misused emergency gear system -- 0.9 percent. CT. Retracted gear prematurely on takeoff -- 2.8 percent. f, Extend gear too late -- 1.8 percent. Initiated bv: AWS-340 w ### Page 2 5 0 PREXENTIClffJOFGEARUPORCOLLAPSEDGEARLANDINGS. a. We remend the following tried and woven landing procedures k~ deter inadvertent heels up or inadvertent gear retraction during touchdown and rollout: (1) c)n the downwind leg, a at the final approach fix inbound, make it a habit ti complete the reqended landing gear &e&list for your aircraft. This accomplishes two purposes. It ensures that action has been taken to lower the gear, and it increases your awareness so y13u can recheck the gear- . down indicators prior to landing. (2) Ccmplete the landing roll and clear the runway before operating any levers or switches unless good operating practices dictate otherwise. This will accomplish the following: The landing gear strut safety switches will be actuated, deactivating the landing gear retract system. After rollout and clearing the runway, you will be able to focus attention on the after landing checklist and to identify the Foperr controls. b. We suggest the following for consideration by the owner/operator: (1) Provide a oondensed checklist, mounted in view a reminder for its use and easy reference. (2) Periodically review the landing gear emergency procedures for your aircraft. (3) Be familiar with the landing gear warning horn and warning of the pilot, as extension light systems of your aircraft. Use the horn system to cross-check the warning light system Men an unsafe oondition is rooted. (4) Review the procedure for replacing light bulbs in the landing gear warning light displays for your aircraft, so that you can properly replace a bulb to determine if the bulb(s) in the display is good. Check to see if spare bulbs are available in the aircraft spare bulb supply before flight. (5) Have known landing gear deficiencies arrected before flight. **REMEMBER, AS A PILDT YOU ARE RESPONSIBLE FDR TKE S&FE OPERATION OF YOUR AIRCRAFT.** 6 l MECHANICALFAILURE. Mechanically-induced failures of retractable landing gear have involved: a. Metal fatigue/failure. b 0 Improper installation of parts. c. Implroperly securred parts. Par 5 ### Page 3 e/8/80 AC 20-34D d l Use of non-standard FtSe e, Rupture of hydraulic lines. fe Failure of electrical wire connections, relays, contactors, and/or actuators. 85 l Malfunctions of warning systems. he Inoperative limit and safety witches, i, Uplocks failed to release. . 3 l Ibdocks failed to engage. k. Wheels jamned or hung up in wheelwells. le Plains have disengaged frcxn sprockets. me Cables fouled in pulleys. n. Slide tubes became bound due tr, mntamination and corrosion. 0. Torque tubes and drag struts wre bent due to excessive loads being applied. Many of those difficulties were adjusmt, lack of lubrication tion and control of Comosioh. found to be the result of improper rigging and and/or an insufficient program for the prevm- 7 PmMAINTNUCEe It is a good practice t; use the information furnished by aircraft manufacturers in servicing your airCIXft. Particular attention should be directed toward keeping the landing gear, wheelwell, and adjacent areas clean and free of md and debris. Dirty switches and valves my cause false safe light indications or interrupt the -tension cycle before the landing gear is cmpletely dam and lOCked, Repair or replace protective boots that are damaged or missing. Oversize or recapped tires my cause landing gear to stick in the wheelwell and prment artensione Assure that shock struts are properly inflated and the pistons are kept clean. Iaibricate landing gear in accordance with the manufacturer's instructions. Wipe off excess grease *en lubricating landing gear system. Establish a program for corrosion prevention and amtrol for your aircraft to preclude its effect upon proper operation/ failure of landing gear structure ad parts. KeepGear Clean 1 Par 6 ### Page 4 8 . REQUIRED MAINTENANCE. During the annual, loo-hour or progressive landing gear inspection cycle, the aircraft is placed on jacks and the gear canpletely inspected for condition, rigging, and woper operation, including the warning system. Intermediate inspection and servicing will further ensure against landing gear system malfunction. 9 a INSPECTIONFREQUENCY. a. How often shall a landing gear system be inspected and serviced? As often as it is necessary ti assure proper function of the landing gear system. At least as often as Federal Aviation Regulations, including applicable Aimrthiness Directives, require. It iS mended that the aircraft *manufacturer% instructions for inspection frequency and procedure be followedo b An ideal time for an interim inspection of the landing gear system would& during the pilot's preflight inspection. c. When aircraft are operated frm rough surfaces or are used for student instruction, more frequent inspections may be in order. when a hard landing is experienced or the gear strikes an object tiile taxiing, it is wise to inspect for damage. Damage may occur and rigging may be affected by sharp turns at high taxi speeds, by faulty technique during a crosswind landing, or by taxiing off a hard surface into deep mud or snow. d Awareness of our human limitations, those of the aircraft w operate, and the proper application of good maintenance practices can effect a substantial reduction in accidents involving retractable landing gear, and a substantial improvement in aviation safety. .Director of Airworthiness Par 8 --- From OpenAirDocs.org, an independent open copy of FAA data. Only the Federal Register edition on govinfo.gov is the official legal text of an AD.