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Accident reports:
Beech C90
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Reviews of accident investigation reports
Read the comments on the investigation reports of the reviewed accidents by clicking any or all of the links below:
To be continued ... |
Reviewed accident investigation reports
Saab SF-340, Netherlands 4 April 1994
Ten minutes after takeoff, an oil pressure warning on the right hand engine made the captain decide to return to the airport. He left the affected engine idling; the propeller was not feathered. The airplane got displaced to the right on short final and at 45 ft RA, the captain decided to go-around, using thrust of engine #1 only; #2 was kept idling.At first, no additional rudder was applied to counter the asymmetric thrust moment; max. aileron could not prevent the airplane from rolling into the idling engine. The airspeed was higher than the AFM-listed VMCA but still, control was lost. The airplane crashed.
The actual VMCA of this
airplane after selecting go-around power was definitely much higher than
the flight manual listed VMCA because VMCA is determined with a feathered (low-drag) propeller,
a small bank angle away from the inoperative engine and with other factors
that have influence on VMCA at their worst case value.
During the go-around, the actual VMCA must have increased above the indicated airspeed which led to
an uncontrollable airplane and a catastrophic accident. The
pilots obvious did not know about VMCA and how to recognize
and 'control' this minimum control speed. VMCA was
not mentioned by the investigators in the formal Accident Report.
The cause of the accident as determined by AvioConsult differs considerably from the cause presented in the formal Aircraft Accident Investigation Report.
A thorough 10-page analysis of this accident, written using the data of the Flight Data Recorder that are included in the formal Aircraft Accident Investigation Report and the knowledge of experimental flight-test techniques that are used to determine VMCA, is available for download:
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Lockheed C-130H, Netherlands 15 July 1996
A C-130 crashed at Eindhoven Airbase in the Netherlands following the failure of engines #1 and #2 due to bird ingestion during a go-around that was initiated just prior to touchdown. Engine #3 was already off before the approach.The go-around (while n-1) was initiated at a speed below 97 kt, which is far below the flight manual required go-around speed of VMCA2 (134 kt in this case). The flight manual requires acceleration to VMCA2 (VMCA for n-2) before selecting full go-around power to be able to maintain control and in anticipation of another engine to fail on the same wing. If two engines fail on the same wing and the power setting on the other engines is high, the airplane will be uncontrollable at speeds below VMCA2.
In this case, the airplane lost the thrust of three engines ( # 1, 2 and 3). Only #4 was operating on max. thrust right after the bird ingestion. In this very special case, the actual minimum control speed was however VMCA1. As the airspeed was even a little below VMCA1, the airplane started to slowly roll and slide away in a direction away from the operating engine, until it impacted the ground.
The pilots of the airplane and the accident investigators did not know about the real value of the minimum control speeds of the airplane, not about the factors that influence VMCA, not how the magnitude of VMCA can be 'controlled' by the pilots and not what VMCA really means for the controllability and safety of flight before and after engine failure, despite the fact that Lockheed provided good VMCA data and explanations, including control limitations, in the airplane flight manual as well as in a very good booklet 'C-130 low speed flying qualities' that is available to all C-130 pilots.
Cause
of the accident
The accident was caused by the pilots
because they ignored the go-around speed warnings in the flight manual
and initiated a go-around at a speed 37 knots(!) below the flight
manual required go-around speed.
An analysis of the accident including comments on the
formal accident investigation report is available for download:
Download
this analysis
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downloads page
Cessna 404, Australia 11 Aug. 2003
Shortly after liftoff, while still over the runway, the right engine failed. The pilot retracted the landing gear, selected flaps up and feathered the right propeller and then, at very low altitude, turned left, into the operating engine, to return for landing. One of the conclusions in the report was: The aircraft was manoeuvred, including turns and banks, at low altitude resulting in a decrease in airspeed below that required to maximise one-engine inoperative performance.While on the left hand downwind leg, the airspeed decayed, the altitude could not be maintained and the airplane descended and impacted with the ground. Weight and cg were within limits.
Cause of the accident
The pilot did not maintain 5 degrees of bank after engine failure
as required in step 6 in the engine failure procedure in the flight
manual, but initiated a turn at both too low an altitude (100 ft AGL)
and while the airspeed was too low. Control was not lost
immediately, because the turn was in the direction of the operating
engine, which is the favorable direction for keeping actual VMCA
low, i.e. below the published VMCA.
The accident investigation report did not include the effect of bank angle on VMCA and the necessity for a 5 degree bank angle into the good engine as a life-saving factor that influences both the controllability and the one engine inoperative climb performance. Pilot and accident investigators were obviously not familiar with the effect of bank angle on both VMCA and the airplane performance, may be because it was never taught to them.
A supplemental analysis to the formal accident investigation report, written by AvioConsult, using experimental flight-test expertise, is available for download:
| Download this analysis | Return to downloads page |
Beech C90, Australia 27 Nov. 2001
Just prior to, or at about the time the aircraft became airborne, the left engine failed. After liftoff, the aircraft remained airborne for about 20 seconds. The aircraft was rolling through about 90 degrees left bank, it struck power lines about 10 m above ground level and about 560 m beyond the end of the runway. It then continued to roll left and impacted the ground inverted in a steep nose-low attitude.Cause of the accident
The accident was caused
because of an
incomplete and deficient engine emergency procedure. In
addition, the real value and meaning of VMCA was neither
clear to the pilot, nor to the accident investigators.
AvioConsult wrote a letter to the CEO of Raytheon Aircraft Company on 8 August 2006 expressing concerns about the definitions and the engine emergency procedures in the operator manual of the Beech King Air C90 and to present recommendations to improve. But Ratheon never responded.
A supplemental analysis to the formal accident investigation report, written by AvioConsult, using experimental flight-test expertise, is available for download:
| Download this analysis | Return to downloads page |
Boeing 737-200, Algeria 6 March 2003
Just after passing V1, an engine failed. Almost immediately after liftoff, control of the airplane was lost and the airplane crashed, killing all but one on-board.AvioConsult reviewed the accident investigation report and concluded that the engine emergency procedures in the Flight Crew Training Manual were inappropriate because the recommended control inputs were not leading to the 10% airspeed safety margin over VMCA that aviation regulations require when an engine fails during takeoff.
When using the recommended control inputs (for keeping the wings level), the actual minimum control speed that the airplane experiences right after liftoff, will be much higher than the minimum control speed that was determined during flight-testing and that is used to calculate both VR and V2. Actual VMCA was most probably even a little higher than V2 at the moment of liftoff; because the airplane continued a slow roll into the dead engine.
Cause of the accident
The accident was caused by inappropriate engine emergency procedures. The pilots are not to be held responsible.
AvioConsult recommended Boeing in July 2005 to improve the procedures, but Boeing responded that 'there was no compelling reason to change the procedures'. Less than two months later, on 5 Sept. 2005, another Boeing 737 crashed following the failure of an engine during takeoff in Medan, Indonesia.
An analysis of the Engine Failure Takeoff Procedures in the Boeing 737-200/300/400 Flight Crew Training Manual is available for download:
| Download this analysis | Return to downloads page |
Piper PA-31, New Zealand, 17 Dec 2002
Shortly after takeoff, the left engine quit operating for unknown reasons. The pilot feathered the propeller and returned to the airport for landing.During the final turn, control was lost and the airplane crashed. According to the report, "the control loss occurred because the pilot probably let the airspeed fall below the minimum single-engine control speed, which brought about an uncontrollable yaw and rapid roll towards the inoperative left engine".
The final turn, a left turn, was a turn into the dead engine while the speed was obviously near or below the minimum control speed VMCA. If indeed the other engine was set to provide high thrust for maintaining the required flight path, the actual VMCA might have increased to a much higher value than the flight manual listed VMCA, because the turn was into the dead engine. The increase of actual VMCA above the indicated airspeed led to an uncontrollable airplane instantaneously, and not only because "the pilot probably let the airspeed fall below the minimum single-engine control speed". A recovery at this low altitude and while maintaining the power setting was and will never be possible.
The airspeed indicator must have been provided (i.a.w. FAR 23) with a red radial line indicating VMCA. But what airplane manuals and placards on the instrument panel do not tell (yet) is that this line is valid only if the bank angle is the same as was used to determine VMCA. A manufacturer may select a bank angle of max. 5 degrees (away from the failed engine) to determine VMCA, but there is no requirement to publish the actual bank angle used for the red-lined VMCA to be valid. Five degrees away from the failed engine will always be safe, though. Not all pilots know or realize that VMCA is no more than a minimum control speed for maintaining straight flight while banking a few degrees away from the inoperative engine and start to maneuver while the power setting on the remaining engine is high, after which control cannot be maintained (if the other variables that have influence on VMCA happen to be at their worst case value too).
Cause of the accident
To the opinion of AvioConsult the accident happened
because the pilot turned the airplane at too low a speed, in the
direction of the inoperative engine, while the power setting on the
operating engine was high. These conditions increased actual
VMCA to a value much higher than the flight-manual listed
and red-lined VMCA and
higher than the indicated airspeed. Loss of control
became unavoidable. Under
these circumstances, control can only be regained by quickly
increasing the speed or, if the altitude is low, by decreasing
the power temporarily just a little bit to decrease the yawing
moment, after which actual VMCA will decrease as
well and control might be regained
while at the actual indicated airspeed. Power can be
increased again as soon as 5 degrees away from the inoperative
engine is established.
The pilot is not to be held responsible though; airplane flight
manuals, student pilot text books and flight schools do not warn
pilots for this VMCA increase. It is a long
forgotten but still very actual and life-threatening 'phenomenon'.
Nevertheless, all experimental test pilots and flight-test engineers
know about this, because it is observed every time a VMCA
is (properly) determined during experimental flight-testing on any multi-engine
airplane.
Similar accidents can be prevented in the future if pilots read the Report
'Airplane Control after Engine Failure' or
attend the accompanying lecture by
AvioConsult and if airplane manufacturers, flight manual
writers and flight schools use the many recommended improvements included
in the report.
| Download this text in pdf format | Return to downloads page |
Piper PA-44-180, Netherlands 14 August 2002
A Piper PA-44-180 Seminole, owned and operated by Martinair Flight School in The Netherlands, crashed in a lake, killing an instructor and two students during a demonstration of flight with an inoperative engine. The Dutch Transport Safety Board thoroughly investigated the accident and concluded that following the intentional shut down of the left engine, the fuel valve of the right engine was inadvertently closed instead of the valve of the left engine, after which the right engine quit as well and an emergency landing became unavoidable, according to the report. The report also concludes that the airspeed decreased below the stall speed, after which control of the airplane was lost at an altitude from which recovery was not possible.But to the opinion of AvioConsult, this was not the cause of the accident. Neither the pilots nor the investigators did know about the limitations of minimum control speed VMCA. A VMCA, although never determined, also exists due to asymmetrical drag caused by one feathered propeller and the other not feathered.
The analysis (in Dutch language) with comments on the formal accident investigation report is available for download:
| Download this analysis | Return to downloads page |
Documentation
review PA-44-180.
The formal accident investigation report did not report on the
training documentation used by the flight school. AvioConsult
therefore asked, and received permission, to review the airplane and
training documents. Many errors and deficiencies were found.
A limited analysis of the PA-44 documents, as used by the flight
school (and also by other PA-44 owners) in the English language, is
available for download:
Download
this analysis
Return to
downloads page
This analysis will also be useful to operators of other multi-engine airplane types.
AvioConsult wrote a letter to
the CEO of The New Piper Aircraft, Inc.
on 9 August 2006 expressing concerns about the imperfections in the Pilot's
Information Manuals of Piper Aircraft and to present
recommendations for improvement.
But the company never responded.
Mitsubishi MU-2B, USA 10 Dec. 2004
Shortly after takeoff, the left engine failed. The pilot returned for landing via a left-hand circuit; the left propeller was feathered. The airplane did overshoot the final approach of runway 35R and was cleared to the next runway 28. The landing lights were then seen turning down toward the terrain. The airplane crashed; the two souls onboard were fatally injured.
Cause
of the accident
The NTSB determined the
probable cause(s) of this accident as follows:
The pilot's failure to maintain minimum controllable airspeed
during the night visual approach resulting in a loss of control and
uncontrolled descent into terrain. A contributing factor was the
precautionary shutdown of the left engine for undetermined reasons.
To
the opinion of experimental flight-test expert AvioConsult, which is based
on the data provided in the report, the real cause of the accident is the
pilot's failure to maintain a small bank angle away from the inoperative
engine while the power setting was increased or was high. This caused
the actual VMCA to increase above the indicated airspeed after
which control was lost. Control could not be regained because of the
low altitude.
The pilot however, is not to be blamed. This
accident was also caused by an incomplete and deficient engine emergency
procedure, by inadequate pilot training on the subject of engine failures,
and by imperfections and errors in FAR's and other publications. The
real value and meaning of VMCA was neither clear to the pilot,
nor to the accident investigators.
A supplemental analysis to the formal accident investigation report, written by AvioConsult,
using experimental flight-test expertise, is
available for download:
Download
this analysis
Return
to downloads page
Boeing 747, Netherlands 4 October 1992
Shortly after takeoff, two engines dropped off the right wing due to fuse pin failure of pylon #3. The pilots decided to return to the airport and initiated a right hand turn in the direction of the dead engines. During the second right hand turn to position for the approach, the airspeed was decreased, obviously to a value below the actual minimum control speed VMCA2, upon which control of the airplane was lost and the airplane crashed in a residential area.The formal accident investigation report does not even discuss the air minimum control speed, may be because in civil aviation regulations (part 25), a minimum control speed for two engines inoperative (VMCA2) does not exist (anymore). But in-flight, it definitely still exists and causes catastrophes if not used.
Why did the pilots (and accident investigators) not know that not maintaining straight flight with a small bank angle away from the inoperative engines is almost certainly deadly when the power setting on the remaining engines is high and the airspeed is (getting) low? Most probably because the engine emergency procedures and VMCA definitions in airplane flight and operating manuals are incorrect or inappropriate / deficient, or because the engine-out training is inappropriate and incomplete. Refer to the Report 'Airplane Control after Engine Failure' that AvioConsult presents on the products page of this website to learn about improving procedures and definitions.
The huge effect of bank angle on VMCA and VMCA2 was not considered by the accident investigators. This effect is calculated and illustrated in Paper 'The Effect of Bank Angle and Weight on VMCA' that is available for download:
| Download this paper | Return to downloads page |
Please also refer to the comments on the Boeing 737 FCTM above.
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