NTSB Factual Report

On August 26, 2010, at time unknown, a Diamond Aircraft Industries Inc. DA 20-C1 airplane, N409AM, exhibited minor damage when a student pilot found a crack on its nose landing gear (NLG) fork during a preflight inspection at the Central Illinois Regional Airport at Bloomington-Normal, near Bloomington, Illinois. Visual meteorological conditions prevailed all day in the area. The operator reported no injuries. The instructional flight was to be operated under 14 Code of Federal Regulations Part 91.

This cracked NLG fork, found by the student pilot during the preflight of the incident airplane, was the third cracked fork that the operator reported since March 30, 2009. The two previous cracked NLG fork occurrences were reported on April 7, 2009 and on March 30, 2009. This recent NLG fork accumulated 573.6 hours of total time before the crack was observed and the two previous forks accumulated 1,306.0 hours and 1,926.7 hours respectively. The incident airplane’s last inspection was a 100-hour inspection and it was completed on July 23, 2010.

The cracks were in similar locations for all three occurrences. The NLG forks’ arms exhibited cracking near the bolt hole that is used to secure the fairing to the NLG fork. The NLG forks' part number (p/n) were: 20-3220-08-00.

The Federal Aviation Administration Service Difficulty Report (SDR) query page was queried to determine how many Diamond Aircraft Industries Inc. cracked NLG forks were reported. There were 12 SDR reports on the NLG forks, which included the three from the incident operator.

Another operator of DA 20-C1 airplanes was contacted in reference to NLG fork cracking. This operator had a fleet of 44 DA 20-C1 airplanes which were also used for flight instruction. A representative for this operator reported that his fleet’s airplanes averaged about 60 hours of flight time per month and that the fleet accumulated 13 cracked NLG forks between February 24, 2009 and July 14, 2010. He said that the NLG forks are replaced and a condition report is submitted directly to the manufacturer, which is their normal procedure for failed parts. Their total time on the forks before the cracks were observed ranged from 595.9 hours to 2,253.9 hours with an average of 1,371.09 hours. The representative further stated that the airplane’s manufacturer recommended the installation of screws in the bolt holes that are used to secure the fairing to the NLG fork. The installation was indicated to reduce a stress concentration point.

Diamond Aircraft Industries Inc. had been working on a design change at the time of the incident with N409AM and subsequently published a Service Information Letter (SIL) 20C1-005. The SIL advised owners, worldwide, that the old NLG fork assembly P/N 20-3220-08-00 had been replaced with the new fork assembly, P/N 20-3220-08-00_1. The SIL further advised customers to install machine screws, pan head, P/N MS35207-282, with Loctite 242 when the wheel fairings are not used to avoid any potential cracking that also may occur at that location. Lastly, the SIL refers owners to the Aircraft Maintenance Manual (AMM), Revision 17, dated November 1, 2010, for new inspection requirements for the NLG. The airplane inspection schedule in the AMM indicated that the NLG is now to be inspected every 100 hours as opposed to the previous revision’s 6,000-hour inspection cycle.

The National Transportation Safety Board, in a letter dated June 3, 1993, to the FAA Administrator, issued recommendations in reference to SDRs. The letter, in part, stated:

The Federal Aviation Administration's Service Difficulty

Reporting (SDR) program is often used during aviation

accident/incident investigations to research the history of

aircraft failures, malfunctions, and defects. However,

attempts to effectively use the SDR data base in recent

Safety Board investigations have revealed that the current

program is incomplete and of limited value in identifying

accurate service defect histories because many reportable

service difficulties are not reported to the FAA. ...

The Safety Board is also concerned that the current efforts to

improve the SDR system do not address the problems with

general aviation Malfunction or Defect (M or D) Reports.

Current Federal Aviation Regulations (FARs) require that

holders of certificates under 14 Code of Federal Regulations

(CFR) Parts 21, 121, 125, 127, 135, and 145 submit reports

of service difficulties to the FAA for entry into the SDR

system. Service difficulty reporting is currently not required

under Parts 43 and 91. This factor may be contributing to

low reporting, which significantly reduces the value and

effectiveness of the program. Encouraging those who operate

under the provisions of 14 CFR Parts 43 and 91 to submit

M or D Reports, and providing appropriate guidance to them,

would improve the quality and content of the general aviation

SDR data base.

The letter included the following recommendations to the FAA:

Review the reporting items and establish standardized

reporting formats for Malfunction or Defect Reports and

Service Difficulty Reports that include the capability for

electronic submission. Encourage all operations under

14 CFR Parts 21, 43, 91, 121, 125, 127, 135, and 145 to

use electronic reporting methods for submission of service

difficulty information. (Class II, Priority Action) (A-93-61)

Encourage all persons or organizations that operate under

14 CFR Parts 43 and 91 to submit Malfunction or Defect

Reports and provide appropriate guidance to improve the

quality and content of the general aviation service difficulty

data base. (Class II, Priority Action) (A-93-62)

Ensure that prompt analysis of service difficulty reports and

dissemination of alerting information is being accomplished

in accordance with Federal Aviation Administration policies

and procedures. (Class II, Priority Action) (A-93-63)

Encourage foreign regulatory agencies to provide service

difficulty data from resident operators and manufacturers to

the Federal Aviation Administration (FAA) for

incorporation into the FAA service difficulty data base.

(Class II, Priority Action) (A-93-64)

The status of these recommendations, at the time of publishing of this incident report, are closed-unacceptable action for A-93-61 and closed-acceptable action for A-93-62, A-93-63, and A-93-64.

NTSB Probable Cause

The cracked nose landing gear fork assembly found during the preflight inspection.