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B712, en-route, Union Start MO USA, 2005 (HF LOC WX)
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| Summary | |
| On 12 May 2005, a Boeing 717-200 being operated by Midwest AL on a scheduled passenger flight from Kansas City to Washington National and climbing in night IMC experienced a sudden loss of control from which recovery was only achieved after a prolonged period of pitch oscillation involving considerable height variation. An en-route diversion to Kirksville MO was then made without further event. None of the 80 occupants were injured and the aircraft was not damaged. | |
 | |
| Event Details | |
|---|---|
| When | May 2005 |
| Event Type | HF, LOC, WX |
| Day/Night | Night |
| Flight Conditions | IMC |
| Flight Details | |
|---|---|
| Aircraft | BOEING 717-200 |
| Operator | Midwest Airlines |
| Domicile | United States |
| Type of Flight | Public Transport (Passenger) |
| Origin | Kansas City International |
| Intended Destination | Ronald Reagan Washington National |
| Actual Destination | Kirksville |
| Flight Phase | Cruise |
| ENR | |
| Location En-Route | |
|---|---|
| Origin | Kansas City International |
| Destination | Ronald Reagan Washington National |
| Location | |
|---|---|
| Approx. | over Union Start, Missouri, USA |
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| HF | |
|---|---|
| Tag(s) | Ineffective Monitoring Manual Handling Procedural non compliance Inappropriate crew response (automatics) |
| LOC | |
|---|---|
| Tag(s) | Degraded flight instrument display Flight Management Error Flight Control Error Environmental Factors Temporary Control Loss Extreme Pitch |
| WX | |
|---|---|
| Tag(s) | In Flight Airframe Icing |
| EPR | |
|---|---|
| Tag(s) | “Emergency” declaration |
| Outcome | |
|---|---|
| Damage or injury | No |
| Causal Factor Group(s) | |
|---|---|
| Group(s) | Aircraft Operation |
| Safety Recommendation(s) | |
|---|---|
| Group(s) | None Made |
| Investigation Type | |
|---|---|
| Type | Independent |
Description
On 12 May 2005, a Boeing 717-200 being operated by Midwest AL on a scheduled passenger flight from Kansas City to Washington National and climbing in night IMC experienced a sudden loss of control from which recovery was only achieved after a prolonged period of pitch oscillation involving considerable height variation. An en-route diversion to Kirksville MO was then made without further event. None of the 80 occupants were injured and the aircraft was not damaged.
Investigation
An Investigation was carried out by the NTSB. It was established that the onset of the loss of control just above FL190 had occurred with the aircraft commander as PF and had followed a progressive loss of airspeed which had not been noticed by the flight crew. IMC had prevailed throughout the recovery which took some 8 minutes and although engine ice protection had been on, airframe ice protection had not been selected on until some 4 minutes after the event began. The initial steep dive led to an overspeed which the First Officer felt was "almost beyond recovery." The flight crew reported that the aircraft had not responded normally or consistently to pitch control inputs and FDR data for the event showed a series of pitch oscillations within altitude range of 10,600 feet3,230.88 m and 23,300 feet7,101.84 m and ground speed variation 290 knots537.08 km/h
149.06 m/s and 552 knots1,022.304 km/h
283.728 m/s.
The aircraft commander was unable to level the aircraft from the initial recovery climb and it entered a second dive, at which point the First Officer called “I’m Flying” and took control and was eventually able to bring the aircraft under control. It was apparent afterwards, however, that the aircraft commander had taken this call and subsequent action as advice that the First Officer` was merely assisting on the controls and so had continued to make inputs and only positively relinquished control of the aircraft to the First Officer (without a formal handover) when he began to communicate with ATC once recovery had been achieved. FDR data showed that this confusion had led to the two control columns being split due to opposite forces being applied.
In respect of the risk of airframe icing, the investigation noted that the actual freezing level was likely to have been in the region of 12000 feet3,657.6 m with conditions conducive to icing prevailing in the area up to 25,000 feet7,620 m. It was estimated that a 40% probability of severe clear icing conditions around 19000 feet5,791.2 m had existed and noted that convective activity would have increased the probability of icing conditions and their severity if encountered.
In respect of the report from the flight crew that there had not been any significant returns on the weather radar, the investigation noted that the low power output and wavelength of these radars makes them prone to attenuation which is further aggravated in precipitation and / or icing conditions. It was calculated that in the prevailing circumstances, sufficient attenuation would have existed to create the ‘green only’ returns reported.
The conclusions of the investigation included:
“Post-incident testing of the airplane's mechanical and electronic systems revealed no abnormalities that would have accounted for the unreliable airspeed indications or the loss of control reported by the flight crew. Post-incident computer modeling also confirmed that the airplane performed in a manner consistent with all deviations from normal flight having been initiated or exacerbated by the control inputs of the flight crew. Review of flight data recorder, cockpit voice recorder, and flight crew interviews revealed that the flight crew's actions during the event were in part contradictory with operator's training and operational procedures.”
And that:
“The crew initially failed to properly identify and respond to the erroneous airspeed indications that were presented and failed to coordinate their recovery of the airplane to controlled flight.”
The Probable Cause of the event was determined by NTSB as “a loss of reliable airspeed indication due to an accumulation of ice on the air data / pitot sensors. Contributing to the incident was the flight crew's improper response to the erroneous airspeed indications, their lack of coordination during the initial recovery of the airplane to controlled flight, and icing conditions.”
The Final Report was approved on 14 January 2009 and may be seen at SKYbrary bookshelf: NYC05MA083
No Safety Recommendations were made.