# NTSB FTW95IA083: Boeing 737-3A4, N326SW, Houston, TX, January 1, 1995

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: January 1, 1995, 11:50 local (17:50 UTC)
- Place: Houston, TX
- Location: 29.7633° N, 95.3633° W: Placed by OpenAirDocs: center of Houston, TX, within about 14 miles (OpenAirDocs)
- Nearby events: https://openairdocs.org/map.md?lat=29.7633&lon=-95.3633&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 66 uninjured
- Status: Completed, report August 31, 1995
- Report: Approved by Office Director
- NTSB case key (mKey): 19263
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW95IA083
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/19263/pdf
- Page: https://openairdocs.org/ntsb/FTW95IA083

## Probable cause

ENCOUNTER WITH WAKE TURBULENCE.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Vortex turbulence encountered, approach
  - wake turbulence - encountered (cause)

## Analysis

DURING DESCENT FOR THE LANDING APPROACH THE PILOT EXPERIENCED UNCOMMANDED ROLL DIVERGENCE.  THE AIRCRAFT WAS AT APPROXIMATELY 240 KNOTS, CLEAN CONDITION, AND POWER WAS REDUCED AT THE TIME OF THE OCCURRENCE.  THE AIRCRAFT WAS FOLLOWING AN MD-80 WHEN THE EVENT OCCURRED.  THE FIRST PILOT WAS AT THE CONTROLS WHEN THE UNCOMMANDED ROLLS OCCURRED, HOWEVER, THE CAPTAIN ASSUMED CONTROL EARLY DURING THE SEQUENCE.  IT WAS NOTED THAT THE AUTOPILOT ALTITUDE HOLD WAS ENGAGED.  THE INITIAL DIVERGENCE WAS A 20 DEGREE RIGHT ROLL.  AS THE RIGHT ROLL WAS DEVELOPING THE PILOT APPLIED A LEFT CORRECTION, AND THE AIRCRAFT ROLLED 30 DEGREES LEFT. THE PILOT THEN APPLIED RIGHT RUDDER WHICH RESULTED IN THE WINGS COMING TO THE LEVEL ATTITUDE.  AN EXAMINATION OF THE FLIGHT CONTROL SYSTEM FAILED TO REVEAL ANY ANOMALIES.

## Factual narrative

On January 1, 1995, at 1150 central standard time, a Boeing 737- 3A4, N326SW, experienced a partial loss of roll control during approach near Houston, Texas.  There was no airplane damage and none of the 5 crewmembers or 61 passengers were injured.  The airplane was operated by Southwest Airlines as Flight 293, scheduled domestic Part 121 service from Dallas, Texas, to the Houston, Texas, Intercontinental Airport.  The airplane was level at 6,000 feet on a standard instrument arrival in visual meteorological conditions decelerating through about 240 knots.

The copilot was flying the airplane when the flight encountered wake turbulence from a MD-80.  Flight 293 was in a clean configuration and power reduced in order to decelerate.  The autopilot was engaged in altitude hold and control wheel steering.  After encountering the disturbed air the airplane began to roll right 20 degrees and the copilot responded with left yoke. The airplane then rolled into a 30 degree left bank and the copilot applied full right aileron, but the roll continued to the left.  The captain took control of the airplane and applied right rudder as he maintained the aileron input.  Control was regained and the remainder of the flight was normal.

Inspection and evaluation of the flight control systems failed to reveal any anomalies.

## Aircraft

- Registration: [N326SW](https://openairdocs.org/deregistered/N326SW-2018-02-13), registration cancelled 2018-02-13, S/N 23690, built 1987 (OpenAirDocs)
- Reported make and model: BOEING 737-3A4
- Registry model: [Boeing 737-3H4](https://openairdocs.org/model/boeing-737-3h4) (registry code 138447K) (OpenAirDocs)
- Registry engine: [CFM International CFM56 series](https://openairdocs.org/engine/cfm-international-cfm56-series) (registry code 13802, turbo-fan) (OpenAirDocs)
- Category: Airplane
- Engines: GE CFM56-3 20000 lbs thrust turbo fan
- Damage: No damage
- Flight: Part 121
- Registered owner: Southwest Airlines Co.
- Airworthiness certificate: Standard, Transport
- Departed: DAL, DALLAS, TX
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 37; commercial, flight instructor, airline transport; airplane ratings: single-engine land, multi-engine land, single-engine sea; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 12,000 total, 8,000 in this make and model, 7,500 as pilot in command, 200 in the last 90 days, 60 in the last 30 days, 8 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day

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.

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