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: w AWS-340 
AC 2C-34D 8/8/80 

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 lMECHANICALFAILURE. Mechanically-induced failures of retractable landing 

gear have involved: 

a. Metal fatigue/failure. 

b 0 Improper installation of parts. 

c. Implroperly securred parts. 

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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 prevm7 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 
AC 20034D 8/8/80 

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