# NTSB LAX98LA104: Boeing 737-242C, N746AS, Reno, NV, March 4, 1998 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: March 4, 1998, 13:15 local (21:15 UTC) - Place: Reno, NV - Coordinates: 39.480159, -119.740722 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.4802&lon=-119.7407&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious, 5 minor, 110 uninjured - Status: Completed, report June 21, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 30044 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX98LA104 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/30044/pdf - Page: https://openairdocs.org/ntsb/LAX98LA104 ## Probable cause Unforecasted and sudden encounter with clear air turbulence when passengers and flight attendants were not secured in their seats. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - In flight encounter with weather, cruise - weather condition - turbulence,clear air (cause) ## Analysis The fight encountered severe clear air turbulence en route at flight level 350 and diverted to Reno, Nevada.. There were no reports of clear air turbulence from other pilots nor was it forecasted. The seat belt signs were off at the time. A review of the flight data recorder indicated that, for the period involved, vertical acceleration (Nz) varied from +1g to +1.5g to -0.07g to +1.3g to +0.86g over a 6-second period. The recorded data also indicated that atmospheric stability existed at flight level 350 several minutes prior to the turbulent onset. There was little or no warning given to the flight crew of the impending turbulent conditions. ## Factual narrative On March 4, 1998, at 1315 hours Pacific standard time, Alaska Airlines Flight 684, a Boeing 737-242C, N746AS, encountered severe clear air turbulence (CAT) at flight level (FL) 350 approximately 90 miles north-northeast of Reno, Nevada. There was no damage to the aircraft. Of the 116 personnel onboard, 3 passengers and 2 flight attendants received minor injuries, and 1 flight attendant suffered a broken ankle. Due to the injuries, the flight diverted to Reno. Visual meteorological conditions prevailed at the time. The flight was operated by Alaska Airlines, Inc., as a non-stop, regularly scheduled domestic passenger flight from Seattle to Las Vegas. According to the operator, en route conditions were smooth up until the event. The Captain noted no turbulence, chop, etc., and there were no reports by other aircraft of any turbulence. After level off, the seat belt signs were turned off and the normal announcement made by the flight crew to keep the seat belts fastened while seated. Normal service was in progress in the cabin at the time of the accident. A review of the flight recorder data indicated that, for the CAT period involved, vertical acceleration (Nz) varied from +1.0g to +1.51g to -0.07g to +1.3g to +0.86g over a 6-second interval. (See enclosed sketch and FDR time histories.) The recorded data also indicated stable atmospheric conditions (Nz = 1.0g) at FL 350 during the several minutes prior to CAT onset. ## Aircraft - Registration: N746AS (not matched to a registry record) - Reported make and model: Boeing 737-242C - Category: Airplane - Serial number: 23123 - Airframe hours: 40001 - Engines: P&W JT8D-17 16000 lbs thrust turbo jet - Damage: No damage - Flight: Part 121 - Registered owner: Alaska Airlines - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, December 8, 1997, 724 hours before - Departed: SEA, SEATTLE, WA - Destination: LAS, LAS VEGAS, NV - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 39; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 10,000 total, 3,000 in this make and model, 120 in the last 90 days, 35 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 305° at 100 knots, gusting 30 - Visibility: 50 statute miles - Lowest ceiling: none - Temperature: -65 °F - Altimeter: 29.00 inHg ## 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 19980304010239A](https://openairdocs.org/incident/19980304010239A), Mar 4, 1998: Boeing 737242C, Reno, NV. Encountered cat enroute at FL350. Diverted to rno. Flight attendant broke an ankle. 7 passengers injured. (.4)the flight encountered sever clear air turbulence… 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.