# NTSB MIA94LA003: Douglas DC-3C, N781T, San Juan, PR, October 7, 1993 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: October 7, 1993, 19:40 local (23:40 UTC) - Place: San Juan, PR - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report September 13, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 37445 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=MIA94LA003 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/37445/pdf - Page: https://openairdocs.org/ntsb/MIA94LA003 ## Probable cause PARTIAL FAILURE OF A WING RIB DUE TO EXFOLIATION CORROSION AND INADEQUATE INSPECTION OF THE AIRCRAFT BY COMPANY MAINTENANCE PERSONNEL. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, landing - flare/touchdown - wing,wing rib - exfoliation (cause) - maintenance,inspection - inadequate, company maintenance personnel (cause) - wing,wing rib - failure,partial (cause) ## Analysis AFTER AN UNEVENTFUL LANDING WHILE TAXIING, THE CAPTAIN NOTICED THAT A SECTION OF THE LEFT WING WAS BENT UP. EXAMINATION OF THE AIRPLANE REVEALED THAT RIB NO. 19 IN THE LEFT WING FAILED CHORDWISE MIDPOINT BETWEEN A ROW OF RIVETS AND NUTPLATES ON THE LOWER ATTACH ANGLE DUE TO EXFOLIATION CORROSION. THE FAA APPROVED 50-HOUR INSPECTION REQUIRES VISUAL INSPECTION OF THE ATTACH ANGLE AND BOLTS BUT DOES NOT REQUIRE REMOVAL OF THE WING TIP. ## Factual narrative On October 7, 1993, about 1940, Atlantic standard time, a Douglas DC-3C, N781T, registered to and operated by Tol Air Services, Inc., under 14 CFR Part 135, flight No. 522, as a nonscheduled, international, cargo flight, was substantially damaged on landing at the Luis Munoz Marin International Airport, San Juan, Puerto Rico. Visual meteorological conditions prevailed at the time and an IFR flight plan was filed for the flight from Santiago, Dominican Republic. The airline transport-rated captain and commercial-rated copilot were not injured. The flight originated about 2 hours 2 minutes earlier. The pilot-in-command stated that the second pilot had landed the airplane and while taxiing, he observed that an outer section of the left wing was bent up. Examination of the airplane revealed that Rib No. 19 of the left wing failed. The failed rib was removed and sent to Douglas Aircraft Company for analysis. Analysis of the rib revealed that it failed chordwise due to exfoliation corrosion midpoint between the rivet line and the nutplate line on the lower horizontal section. According to McDonnell Douglas personnel, the location of the corrosion could not be observed by a flightcrew when performing a walk around inspection but can be observed during the FAA approved 50-hour inspection. Review of the FAA approved 50-hour inspection checklist used for the inspection specifically states to inspect all interior structures for corrosion, damage condition and security. Additionally, the outer wing attach angles and bolts are required to be inspected. ## Aircraft - Registration: [N781T](https://openairdocs.org/deregistered/N781T-2015-05-21), registration cancelled 2015-05-21, S/N 4306, built 1943 (OpenAirDocs) - Reported make and model: DOUGLAS DC-3C - Registry model: [Douglas DC3C](https://openairdocs.org/model/douglas-dc3c) (registry code 3021457) (OpenAirDocs) - Registry engine: [Pratt & Whitney R-1830 series](https://openairdocs.org/engine/pratt-whitney-r-1830-series) (registry code 52020, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 4306 - Airframe hours: 36964 - Engines: P&W R1830-92 1200 horsepower reciprocating - Damage: Substantial damage - Flight: Part 135 - Registered owner: Tol Air Services, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: AAIP, September 4, 1993, 39 hours before - Departed: MDST, SANTIAGO, OF - Flight plan: IFR - Airport: SJU, Luis Munoz Marin Int'L, runway 10, 8,016 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 30; commercial, airline transport, private; airplane ratings: single-engine sea, single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 2,450 total, 669 in this make and model, 1,715 as pilot in command, 164 in the last 90 days, 58 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Dusk - Wind: 90° at 6 knots - Visibility: 13 statute miles - Lowest ceiling: 28,000 ft overcast - Temperature: 81 °F, dew point 73 °F - Altimeter: 29.00 inHg - Observed at: SJU, 1 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19931007052509A](https://openairdocs.org/incident/19931007052509A), Oct 7, 1993: Doug DC3C, San Juan, Puerto Rico, Substantial damage. During taxi to ramp noticed outer section left wing was bent up. Had failed cordwise due to corrosion. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.