Narrative:
N138BF was the first of two conforming prototypes of the SJ30-2 business jet. The aircraft departed San Antonio for flight test number 231 for flight flutter certification. The first flutter mission, flight test number 230, was flown one day earlier with the same pilot onboard. The pilot terminated the flight after an uncommanded roll to the left, and a subsequent discrepancy was noticed between his displayed airspeeds and those reported by a chase plane pilot. After takeoff, the airplane climbed to 39,000 feet and set up for a shallow dive along a 090-degree track. This time no problems were noted. The airplane subsequently turned back to the west and began to climb back to 39,000 feet to set up for another dive to the flight test point along a 270-degree magnetic track. This run also was uneventful. The pilot was then cleared to the next test point. However, the pilot did not acknowledge the clearance, but instead, reported that the airplane was rolling to the right, and he couldn't stop it. About 30,000 feet, the test airplane began rolling to the right. The rolling maneuver appeared to be stable, and continued unchanged until ground impact. The airplane rolled about 7 times during a 49-second timeframe, from about 30,500 feet until a near-vertical ground impact.
Although the manufacturers engineering analysis (which did not include any high-speed wind tunnel testing) had predicted positive lateral stability up to Mach 0.90, lateral control was lost during the accident flight below that speed. After the accident, the company conducted high-speed wind tunnel tests, and found that lateral stability decreased with increasing Mach and angle of attack (AOA). Lateral stability became negative (unstable) above Mach 0.83, and rudder input intended to augment lateral trim above a certain Mach could aggravate the situation.
PROBABLE CAUSE: "The manufacturer's incomplete high-Mach design research, which resulted in the airplane becoming unstable and diverging into a lateral upset."
| Status: | Accident investigation report completed and information captured |
| Date: | Saturday 26 April 2003 |
| Time: | 10:05 |
| Type: |  Sino Swearingen SJ30-2 |
| Operator: | Sino Swearingen |
| Registration: | N138BF |
| MSN: | 002 |
| First flight: | 2000 |
| Total airframe hrs: | 284 |
| Engines: | 2 Williams International FJ44-2A |
| Crew: | Fatalities: 1 / Occupants: 1 |
| Passengers: | Fatalities: 0 / Occupants: 0 |
| Total: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Destroyed |
| Aircraft fate: | Written off (damaged beyond repair) |
| Location: | 16 km (10 mls) N of Loma Alta, TX ( United States of America)
|
| Phase: | Maneuvering (MNV) |
| Nature: | Test |
| Departure airport: | San Antonio International Airport, TX (SAT/KSAT), United States of America |
| San Antonio International Airport, TX (SAT/KSAT), United States of America |
N138BF was the first of two conforming prototypes of the SJ30-2 business jet. The aircraft departed San Antonio for flight test number 231 for flight flutter certification. The first flutter mission, flight test number 230, was flown one day earlier with the same pilot onboard. The pilot terminated the flight after an uncommanded roll to the left, and a subsequent discrepancy was noticed between his displayed airspeeds and those reported by a chase plane pilot. After takeoff, the airplane climbed to 39,000 feet and set up for a shallow dive along a 090-degree track. This time no problems were noted. The airplane subsequently turned back to the west and began to climb back to 39,000 feet to set up for another dive to the flight test point along a 270-degree magnetic track. This run also was uneventful. The pilot was then cleared to the next test point. However, the pilot did not acknowledge the clearance, but instead, reported that the airplane was rolling to the right, and he couldn't stop it. About 30,000 feet, the test airplane began rolling to the right. The rolling maneuver appeared to be stable, and continued unchanged until ground impact. The airplane rolled about 7 times during a 49-second timeframe, from about 30,500 feet until a near-vertical ground impact.
Although the manufacturers engineering analysis (which did not include any high-speed wind tunnel testing) had predicted positive lateral stability up to Mach 0.90, lateral control was lost during the accident flight below that speed. After the accident, the company conducted high-speed wind tunnel tests, and found that lateral stability decreased with increasing Mach and angle of attack (AOA). Lateral stability became negative (unstable) above Mach 0.83, and rudder input intended to augment lateral trim above a certain Mach could aggravate the situation.
Probable Cause:
PROBABLE CAUSE: "The manufacturer's incomplete high-Mach design research, which resulted in the airplane becoming unstable and diverging into a lateral upset."
Accident investigation:
 |
|
Classification:
Loss of control
Sources:
» NTSBPhotos
Map
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
The Aviation Safety Network is an exclusive service provided by:
Quick Links:
| ASN Home | Send Correction / Feedback |
| FSF Home | Disclaimer | Copyright |
| Contact Us | Privacy Policy |
| Press / Media |
CONNECT WITH US:
©2023 Flight Safety Foundation