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Products page contents: Why accidents after engine failure? Controlling airplanes after engine failure Paper Airplane Control after Engine Failure Paper The Effect of Bank Angle and Weight on VMCA Paper Staying Alive with a Dead Engine Paper Imperfections and Deficiencies in FAR and CS
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| Download this paper from the Downloads Page |
Coming
soon, a paper for accident investigators:
Analysis of engine failure related accidents after engine failure
Would you like to be notified? Send an e-mail.
Why do accidents after engine failure happen?
Because many pilots have a different understanding of the minimum control speed (VMCA) of an airplane than airplane design engineers, experimental test pilots and flight test engineers. Many pilots are not (yet) aware of the conditions and operational limitations that apply after engine failure for VMCA to be valid, when the airspeed is low and the remaining engine(s) are set to produce maximum thrust.
In a nutshell,
this
is how VMCA is determined during
flight-testing:
After shutting down an engine and the opposite engine set for maximum
takeoff thrust, the airspeed is slowly reduced, while keeping the wings
level until the heading can no longer be maintained with full rudder.
This airspeed is wings-level-VMCA. Then, the bank angle is
increased to 5 *) degrees away from the inoperative engine, after which the
airspeed can be further reduced until again the rudder deflection is maximum
and the heading cannot be maintained. The airspeed at which this
happens is the VMCA of the airplane that will be listed in the
Flight Manual and marked on the airspeed indicator and on a placard, and
is on
big airplanes used for calculating VR and V2.
If, while the indicated airspeed is VMCA and the thrust on the
operating engine(s) is high, the pilot rolls the airplane away from the
favorable 5 degree bank angle to wings level or further, then the heading
cannot be maintained: directional control is lost. A sideslip will
build up immediately reducing airspeed and climb performance. Some
airplanes will still have roll control power to return to the favorable bank
angle, but this is not tested, and cannot be counted on. While banking
5 degrees away from the inoperative engine, the sideslip angle is smallest, hence the drag is lowest and the
remaining climb performance maximal.
On small airplanes it is essential to maintain 5 degrees of bank away from
the inoperative engine. Modern turbofan airplanes might still be able
to climb with the wings level.
Turning at airspeeds as low as VMCA while
the thrust setting is high is deadly!
*) At this bank angle, the sideslip angle is zero, hence the drag is as loow as possible and the climb performance maximal. On big airplanes, the bank angle needs only be between 2 and 4 degrees. The tail design engineer used this bank angle durin sizing the vertical tail.
So, quite an important and life saving limitation/ condition applies when the indicated airspeed is, or is close to VMCA: immediately attain and maintain a small bank angle of 3 - 5 degrees away from the inoperative engine and accelarate and climb straight ahead to a safe altitude first. Do not turn!
The papers presented below explain in detail the controllability after engine failure and presents the variables that have effect on VMCA. A rowboat will serve as an example to begin with.
| Please do not start flight-testing VMCA yourself; testing can be dangerous! |
Similarity between the controllability of an airplane and a rowboat after 'engine' failure
If you are in a rowboat and one of the side-by-side sitting oarsmen quits rowing while the remaining oarsmen continue at maximum effort, the propulsion has become asymmetrical causing the rowboat to start turning (yawing). The helmsman will deflect the rudder to avoid the yawing, but the rudder is effective only down to the speed at which the maximum rudder deflection is reached. This speed is called the minimum control speed (Vmc) of this rowboat.
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To reduce the yawing moment due to the asymmetrical propulsion (NT) and therewith achieve the lowest possible Vmc for maintaining the heading, the helmsman could ask the oarsman who quit to move a little to the side of the oarsman next to him, to shift the center of gravity of the boat towards the attaching points of the working oar, therewith reducing NT a bit. The boat will tip over a little into the working oarsman. While at the same speed, the yawing moment generated by the rudder (Ndr) can be smaller, so the rudder needs not be fully deflected anymore. Hence, the speed could be further decreased until the rudder is again maximum deflected for maintaining a straight course; the minimum control speed is lower for the same rudder size, by just tipping over the boat a bit (shifting the center of gravity) away from the 'failed' oarsman. |
Changing the longitudinal center of gravity affects
the rudder generated yawing moment (Ndr) as well, because the moment arm, the
distance from cg to rudder, changes. Moving the center of gravity aft
decreases the rudder moment arm, making the rudder les effective, so a higher
speed is required to maintain a straight course; Vmc becomes higher.
An aft cg is therefore the worst case.
While the boat is tipping over a few degrees away from the failed oarsman, a
side component of the weight develops in a direction opposite of the rudder
generated side force, reducing the sideslip (drift) and therewith the drag
to a minimum.
For multi-engine airplanes, this similar
characteristic is used for designing and sizing the vertical tail.
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The
gondolas in Venice, Italy are built and operated similarly. The hull
is not symmetrical, for a purpose. Gondolas are
propelled by only a single oar which attaches to the right-hand side of
the stern; that is where the 'thrust' acts (blue arrow). This
asymmetrical thrust causes a yawing
moment that would continue to turn the gondola to the left. The gondolier always stands on the left hand side of the gondola, making the gondola tip over a little, resulting in a side force to the left. In addition, the center of gravity moves to the left causing the moment arm of the oar to the center of gravity to increase and therewith the yawing moment. A continuous turn would result; the gondola would be out of control. To
avoid this undesired yawing, the hull of the gondola is given a
longitudinal asymmetry, as shown in the figure. The
left side of the gondola is designed to displace more water,
providing more 'lift' than the right side, reducing the tipping over
if the gondelier stands on his place. The left side is
made of lighter materials, resulting in a center of gravity that is
no longer in the middle, but to the right, therewith decreasing the
moment arm to the 'thrust' line and decreasing the 'thrust' yawing
moment. The total yawing tendency of the gondola to the left is
decreased, which makes it easier to
maintain a straight course in the narrow canals in Venice. |
The
size of the rudder, the magnitude of the thrust asymmetry, the tipping angle
and the location of the center of gravity play an
important role for the magnitude of Vmc of a rowboat.
On a multi-engine
airplane this is not different, although the loss of directional control
leads to an uncontrolled descend, while a boat remains afloat. Tipping
over to the good engine' side in an airplane can be easily achieved by banking using
the ailerons, rather than shifting weight laterally, like in a rowboat;
airplane passengers have their seatbelts fastened.
Hence, the bank angle of an asymmetrical powered airplane is an important variable as well. This
will be further explained in the next paper.
Controlling Airplanes after Engine Failure
Tail Design Imposed Limitations
| It is recommended to read this free 3-page paper first: |
Multi-engine airplanes are designed, flight tested and certified to continue to fly safely after engine failure or while an engine is inoperative. After reviewing many accident investigation reports using the knowledge gained at the USAF Test Pilot School, it was noticed that most pilots and accident investigators explain and use the minimum control speed VMC in a different way than airplane tail design engineers, experimental test pilots and flight test engineers do. This difference in interpretation has, to the opinion of AvioConsult, often led to catastrophic accidents caused by the loss of control and/or performance after engine failure and also to incorrect and incomplete conclusions and recommendations in accident investigation reports.
The objective of this paper is to prevent accidents following the failure of an engine. To achieve this, a few aspects of the design of the vertical tail of a multi-engine airplane and of the flight test techniques that are used to determine the minimum control speed VMCA (Vmc in the Air, or Airborne) are discussed for the readers to become aware of the real value of VMCA that is listed in Airplane Flight Manuals (AFM) and to learn about the conditions for which VMCA is valid and about the VMCA-related deficiencies that exist in AFM's, training manuals and engine emergency procedures.
Conclusions of the paper: The
vertical tail of multi-engine airplanes is designed and sized only for
maintaining straight flight after engine failure down to the AFM listed
minimum control speed VMCA, while maintaining a bank angle of 3 -
5 degrees (as opted by the manufacturer for sizing the vertical tail) away from the inoperative engine
and while the power setting of the opposite engine is max. takeoff.
However, this essential and life-saving bank angle condition for the AFM listed VMCA
to be valid is regrettably not included anymore in the operational
limitations and engine emergency procedures of most multi-engine airplanes
and not in training books either. In addition, the definitions of VMCA
in AFM's and training manuals are usually not i.a.w. the tail design
criteria and VMCA flight test techniques. Pilots, unaware of
these conditions, perform maneuvers, while the airspeed is at or above the
AFM-listed VMCA when an engine is inoperative, that the
airplane was not designed to do, which has led and will lead again to
catastrophic accidents, unless improvements are made.
While
maintaining the small 3 to 5 degree bank angle away from the inoperative
engine (not just max. 5 degrees without specifying
the direction, as listed in most flight manuals), not only the actual VMCA is lowest, but also the
sideslip angle is smallest, so the drag is lowest possible,
leaving maximum available climb performance while an engine is inoperative.
Refer to the paper presented below for many suggestions to improve airplane
control after engine failure, including regulations, manuals, procedures and
training for flight with an inoperative engine.
The Dutch magazine Piloot en Vliegtuig (Pilot and Airplane) published this article in their December 2008 issue.
| Download this paper | Return to Downloads page | |
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| A few examples: | ||
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VMCA.
On
the airspeed indicator of Part 23 twin-engine airplanes, the
standardized AFM-listed VMCA is indicated by a red radial
line, in this example at 80 kt. However, neither a placard on the
instrument panel nor
a note or warning in the AFM tells the pilot that this VMCA
is valid
only
if a bank angle of 3 to 5 degrees (to be specified by
the manufacturer) is maintained away from the inoperative engine.
Any other bank angle can lead to a much higher actual
VMCA and to the loss of control after which an accident cannot
be avoided. If the pointer is at or near the red line and the thrust on the remaining engine(s) is maximum, only straight flight should be maintained while maintaining a bank angle of 3 to 5 degrees away from the inoperative engine, in all phases of flight. |
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This note is included in the legend of the Climb Performance Chart - One Engine Operating in the Piper PA-44 Pilot's Information Manual. It is included, because not maintaining this bank angle renders the presented performance data invalid; the airplane might not even be able to maintain altitude. Keeping the wings level or turning means loss of performance; altitude cannot be maintained on most multi-engine airplanes if this NOTE is neglected. The reason why this NOTE is included is explained in the downloadable papers presented above and in the paper presented below. | |
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This placard is installed in full view of pilots of Part 23 airplanes to comply with Aviation Regulations (23.1563). The required small bank angle for the listed VMCA to be valid is regrettably not included on the placard, because this is not required by the Aviation Regulations. Not maintaining the small bank angle at airspeeds as low as VMCA, while the power setting of the remaining engine is high, is the real cause of most engine failure related accidents. | |
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VR and V2MIN. The standardized, AFM-listed VMCA is one of the factors for calculating the rotation speed VR and the minimum takeoff safety speed V2MIN of big Part 25 airplanes. Since this VMCA is valid only while maintaining a bank angle of 3 to 5 degrees, as to be specified by the manufacturer, away from the inoperative engine, both the calculated VR and V2MIN are also valid only when maintaining the same bank angle (when the thrust setting is maximum takeoff). |
| This figure, a safety improving suggestion of AvioConsult, shows that the actual VMCA in this example has become higher than VR because the wings are kept level. Bank angle and rudder advisories are presented to decrease the actual VMCA to a safe level to prevent the loss of airplane control. The bank angle advisory widens up as airspeed increases. | |
Control after Engine Failure
This paper,
before 2005 called 'Prevention of Airplane Accidents after Engine Failure',
presents almost all there is to know about flight with an
inoperative engine and was prepared
using the knowledge that formally trained
experimental test pilots and flight-test engineers have on the subject
and on the proper flight test techniques to determine VMCA
and is
intended for pilots, instructors, teachers, aviation authorities,
accident investigators, etc.
The paper (20 pages,
20 figures) includes
all of the following subjects:
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airplane control after engine failure;
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variable factors that influence minimum control speed VMCA;
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flight-testing VMCA and the airplane configuration used;
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the apparent safety of takeoff safety speed V2;
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imperfections and deficiencies in flight manuals and text books on the subject engine failure and flight with an inoperative engine.
Included in the paper are many ready-to-copy recommendations to improve:
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engine emergency procedures;
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flight manuals;
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student pilot textbooks;
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engine-out training.
AvioConsult believes
this paper was necessary because too many unnecessary accidents are happening
following the failure of an engine.
This paper is available for download:
| Download this paper | Return to Downloads page |
In case
you are interested, a two to four hour
lecture
on the subject of Airplane Control After Engine Failure is
available, please contact
AvioConsult.
Besides to the
European Aviation Safety Seminar (EASS) of the Flight Safety Foundation,
a lecture was recently presented to
the airplane accident investigators of the Dutch Transportation Safety
Board. An earlier, less extensive version was presented in a meeting
with the Engine and Propeller Directorate
of the FAA and ALPA, to the Flight Safety Committee of the Dutch Airline Pilot
Association, to the Netherlands Association of Aeronautical Engineers, the Air Forces Flight
Safety Committee Europe and to
Air Force and Navy.
Please
refer to the accidents page
for a number of accident descriptions.
The Effect of Bank Angle and Weight on VMCA
In the paper Airplane Control after Engine Failure, presented above, graphs showing the effect of bank angle and weight on VMCA and on takeoff safety speed V2 are included. These graphs were calculated using a prediction method that is also used by experimental test pilots and flight test engineers before performing the flight-tests to determine VMCA in order to learn about limitations, etc. that might be encountered during the test. This paper presents the prediction method and includes a few data figures. This method can be used for all multi-engine airplanes, provided the required stability derivative data are available.
This paper is available for download:
| Download this paper | Return to Downloads page |
Staying Alive with a Dead Engine
A paper by AvioConsult, presented at the European Aviation Safety Seminar (EASS) of the Flight Safety Foundation (FSF) on 14 March 2006 in Athens, Greece.
Abstract: During flight-testing multi-engine airplanes while an engine is inoperative, the manufacturer may opt to use a small bank angle (max. 5 degrees away from the inoperative engine) to determine the minimum control speed VMCA that is to be listed in flight manuals as an operational limitation and that is used to calculate takeoff safety speed V2.
However, any deviation
from this bank angle increases the actual VMCA.
Keeping wings level increases VMCA
already by some 8 kt; banking into the dead engine increases VMCA
much more. But the airline
pilot does not get to know which bank angle was used and should be
maintained for the listed VMCA
to be valid, because there is no requirement in FAR's 23 and 25 to
present this bank angle in the Airplane Flight Manual. Manuals
currently concentrate on the loss of performance after engine failure,
not on maintaining control.
Many pilots also believe that takeoff safety speed V2 is a
safe speed after engine failure. V2 however, is calculated using VMCA (and VS). If the pilot
does not maintain the bank angle that was used to determine VMCA,
then the actual VMCA
might increase to a value higher than V2: control will be
lost.
Not maintaining the bank angle used to determine VMCA after engine failure during takeoff or go-around
can make the difference between life and death.
This paper is a much abbreviated version of the paper 'Airplane Control'
presented above.
This paper is available for download:
| Download this paper | Return to Downloads page |
Imperfections in FAA and EASA Regulations
A paper by AvioConsult that resulted from the research for the papers presented above. It presents and explains many errors found in aviation regulations and includes ready-to-copy suggestions for improvement.
| Ask AvioConsult for this paper | Return to Downloads page |
Support
In case you are interested in having AvioConsult verify and/ or improve your Flight Manuals, engine emergency procedures, textbooks, accident investigation reports, etc. on the subject, please contact AvioConsult.
Downloads
Comments and downloads on several accident investigation reports and training material, can be found here. The comments were written using the knowledge from the papers and the reports presented above.
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