Investigation report
D6/2009L
Emergency landing by EXTRA EA 300/L aircraft G-EXEA
in Janakkala, Finland on 18 July 2009
Translation of the Finnish original report
G-EXEA
Extra EA300/L
According to Annex 13 of the Civil Aviation Convention, paragraph 3.1, the purpose of aircraft accident and
incident investigation is to prevent accidents. It is not the purpose of aircraft accident investigation or the investigation report to apportion blame or to assign responsibility. This basic rule is also contained in the Investigation of Accidents Act, 3 May 1985 (373/85) and European Union Directive 94/56/EC. Use of the report for reasons other than the improvement of safety should be avoided.
Because of the nature of this incident, the report does not follow the format specified in ICAO Annex 13.
AIB Finland uses the format recommended in Annex 13 for investigation reports published in series A, B
and C.
INVESTIGATION NUMBER: D6/2009L
INVESTIGATION COMPLETED: 4 June 2010
INVESTIGATORS: Hans Tefke
Esko Lähteenmäki
Time of incident:
18 July 2009 at 12:00
Location:
Tervakoski, Janakkala, Finland
Aircraft type:
Extra EA300/L
Registration:
G-EXEA
Engine:
Lycoming AEIO-540-L1B5
Manufactured:
25 February 1998
Purpose of flight:
Aerobatics practice
Damage to aircraft:
Significant
Number of persons on
board:
1
Pilot:
Pilot in command:
Licences:
PPL, SEP (land)
Flying experience:
Total: 728 h
On type: 174 h
Weather:
2
Weather at emergency landing site was sunny. Cumulus
clouds 3/8, wind about 300 degrees, 6 knots. Temperature
23ºC, dew point 9ºC.
SYNOPSIS
Tekstiä An EXTRA EA 300/L aerobatic aircraft, registered G-EXEA, sustained significant
damage in an emergency landing in Tervakoski village, Janakkala, Finland on 18 July 2009
at 13.50 Finnish time. The pilot, who was the sole occupant of the aircraft, suffered only
minor injuries.
Accident Investigation Board Finland (AIB) appointed Hans Tefke and Esko Lähteenmäki
as investigators for the accident.
The aircraft was initially examined at the emergency landing site, after which it was disassembled and transported to Helsinki-Vantaa Airport for detailed inspection. The fuel system
components were removed and their operation was tested at Patria Aviation’s repair shop
in Kuorevesi.
The German accident investigation authorities (BFU) appointed investigator Thomas Kostrzewa as their accredited representative.
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FACTUAL INFORMATION
1.1
Accident flight
The pilot came to Hyvinkää aerodrome on 18 July 2009 around midday. He took
the aircraft out of the hangar and made a pre-flight check, which also included
draining any water from the fuel system. No water or other contaminants were
found in the samples. According to the pilot, the acro & centre tank was ½ full and
the wing tanks ¼ full of fuel. The pilot taxied the aircraft to the refuelling site and
added about 18 l of fuel into the centre tank, filling the tank up.
After refuelling, the pilot and a passenger departed for a flight. Engine test run before take-off was normal. The passenger wanted to take a short flight and they
only flew for six minutes, including take-off, landing circuit and landing. After the
passenger got off, the pilot started the engine again, succeeding at second attempt. When the engine was running, the pilot leaned the mixture by pulling the
mixture control lever back about two inches. As the pilot increased power for taxiing, the engine failed to accelerate but remained at idle. When the pilot pushed
the mixture control fully forward, the engine accelerated normally. During taxiing
the pilot leaned the mixture again, but this did not affect engine performance.
The pilot waited for a while before the runway was vacated and made a pretakeoff check. Take-off and climb were uneventful. During climb and level flight
the pilot used an engine power setting of 25 inHg, rotation speed 2500 rpm and
fuel flow rate 60 l/h. When the pilot was flying north of Riihimäki at about 1500 ft,
he switched the fuel feed from the centre tank to the wing tanks. After reaching
the practice area near Janakkala, approximately 20 km north of Hyvinkää aerodrome, he switched back to the centre tank. Then he climbed higher and made
barrel rolls to the left and to the right. After the rolls he tightened the seat belts,
which had a tendency to loosen.
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Before continuing to practice aerobatic manoeuvres, the pilot chose a field facing
north to south as a possible emergency landing site. He flew over the field and
checked it; it looked dry and the grass seemed short. After that the pilot went on
with aerobatics and flew a loop. At the final stage of the loop, engine power
dropped to idle and the engine stopped responding to throttle lever movements.
The pilot then switched the electric fuel pump on and selected the wing tanks,
which somewhat improved engine performance. He turned towards Hyvinkää at
about 2000 ft and the engine was still running rough. At this stage he called ”mayday” at Hyvinkää aerodrome frequency, reporting an engine malfunction and stating that he would land on a field. During descent the pilot moved the throttle lever
back and forth and switched back to the centre tank. This essentially improved
engine performance, and the pilot reported on the radio that the engine had restarted. However, immediately after this the power dropped back to idle and the
pilot initiated a turn towards the field he had chosen earlier. He called ”mayday”
again and described the location of the emergency landing site. On base leg the
pilot pulled the mixture lever to full lean, turned master switch off and closed the
fuel cock. On approach the pilot noticed that the grass was taller than he had
thought. During landing run the aircraft rolled over and came to rest inverted.
After landing the pilot reported on radio that he had made an emergency landing
but was not injured. He walked to a nearby farm, to which an ambulance had already been called.
Picture 1. The emergency landing site
1.2
Injuries to persons
The pilot’s neck was sore after the incident.
1.3
Damage to aircraft
The aircraft wingtips, canopy, vertical stabiliser, propeller, engine cowlings, engine
attachment and wheel fairings were broken.
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1.4
Other damage
Grass was flattened under the landing path and trampled at the site where the aircraft was disassembled.
1.5
Emergency landing site
The field section is 1380 m long, 150 m wide and facing north-west to south-east.
The surface was hard and the grass was about 110 cm high. The aircraft touched
down approximately 310 m from the south-east end of the field. The landing run
was about 65 m.
1.6
Engine Reassembly
Engine was under maintenance during spring 2009 and it was released to service
May 6th 2009. Reason for this maintenance was mandatory service bulletin MSB
569A from engine manufacturer regarding crankshaft replacement. It was noticed
during engine disassembly that valve guides in cylinders 3 and 5 were worn out of
their limits. These valve guides were replaced. Engine accessories were not replaced while having some running and calendar time left. Test flight was flown
May 8th 2009.
According to the aircraft owner there occurred magneto drop while testing the
magnetos at engine pre-flight test run. The problem disappeared after cleaning
the spark plugs. This happened before the engine was in maintenance in spring
2009.
1.7
Fuel system
The aircraft has two independent tank systems. There are wing tanks in both
wings, total capacity 154 l. All fuel in the tanks can be used in flight. The fuel
quantity indicator is common for both tanks. Each tank has a separate fuel filler
opening. According to the flight manual, the tanks must be empty when performing aerobatic manoeuvres.
The centre tank is located in the fuselage in front of the cockpit. Underneath the
centre tank is a fuel tank for inverted flight with a capacity of 9 l. The total capacity
of both tanks is 51 l, of which 5.5 l is unusable fuel. The tanks are connected with
each other. The centre tank has its own fuel quantity indicator and filler opening.
The aircraft operating manual recommends that the centre tank be used during
take-off and landing.
All tanks are equipped with breather tubes. There is one drain valve for both wing
tanks and one for the centre and inverted flight tank together. The fuel selector
has three positions: wing tanks, centre tank and closed. After the selector valve,
there is a fuel filter, electric pump, engine-driven fuel pump, fuel control unit, distributor valve and nozzles.
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Picture 2. Schematic diagram of the fuel system
1.8
Technical investigations
1.8.1
Inspection of fuel system in fuselage and wings
The fuel system had been emptied at the emergency landing site when the aircraft
was disassembled. There was a total of 5 litres avgas in the wing tanks and about
40 litres in the fuselage tank. The fuel system was visually inspected. All pipes
and tanks were intact and no signs of fuel leakage were detected. The elastic balanced suction pipe in the inverted flight tank was removed and inspected, but no
abnormalities were found in the operation of the pipe or the fuel tank. All fuel pipes
and breather tubes were examined by blowing through and none of them was
found blocked. The operation of the fuel selector valve was tested; it was normal
in all three positions. The fuel filter drain cup and filter net were removed and
found to be clean. The electric fuel pump was removed from the firewall for functional testing.
1.8.2
Engine inspection
The engine was inspected visually. A small amount of grass was found in the engine bay as a result of the emergency landing. The upper side of the firewall was
buckled and the lower engine attachment brackets were broken. All spark plugs
were removed; they were in good condition, but some of the plugs had oil stains.
The cylinders were subjected to a leakage test, which showed normal compression for each cylinder. When the propeller was turned manually, the crank mechanism and accessory gearbox rotated normally.
Magneto timing was correct and the release switch operated normally. Both magnetos were opened and checked; no abnormalities were found.
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The engine driven fuel pump was removed and opened. Two pieces of metal cut
off from the bronze sealing ring were found in the seal compartment of the pump.
The seal compartment also showed marks from sideward movement of the steel
counterplate for the bronze seal. The steel lamina of the pump and their rotation
chamber were in working condition. The investigators sent a letter to the pump
manufacturer, asking about the probable damage mechanism and the effect of the
damage on the functioning of the pump. The pump was assembled for a functional
test. An air pipe located in the engine bay below the pump had stains, possibly
from fuel colourant.
Picture 3. The attachment brackets of the fuel pump bronze sealing ring had broken off.
Picture 4. The thin arrows show the places where the attachment brackets had
been broken off. The thicker arrows show the impact marks caused by sideward
movement of the steel counterplate.
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The fuel control unit, distributor valve, nozzles with attached tubes and engine
fuel system pipes were removed for functional testing.
The oil filter (metal net) was removed and inspected. The filter was clean and intact. The aircraft does not have a regular air filter, but only a coarse metal net.
There was soil in the metal net, and the fuel control air flap and air duct were
partly covered by sand dust.
Picture 5. Engine inlet air metal net, mesh size 1.6 mm
Picture 6. Dirty air flap and air duct of the fuel control unit
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1.8.3
Testing of engine fuel system components
The fuel system components were subjected to a functional test at Patria Aviation’s repair shop in Kuorevesi, using a test bench intended for testing and adjustment of Bendix fuel control units.
The components tested were the Bendix RSA 10AD1, s/n 70154304 fuel control
unit, fuel system distributor valve and nozzles, mechanic fuel pump Lear Romec
p/n RG9080J4A, s/n D9155 and electric fuel pump Weldon Pump p/n B 8120-M,
s/n 80114.
The values for the fuel control unit were as specified in the maintenance manual.
A flow test performed on the distributor valve and nozzles showed that when the
pressure reached about 10 psi, test fluid started to bubble from the vent hole on
top of the distributor valve. However, the leakage was minor and was coming
through the diaphragm attachment screw threads. All nozzles were operating
normally.
When the mechanic fuel pump was connected to the test bench, it was noticed
that test fluid was leaking through the vent hole for the pump drive shaft seal
chamber. Leakage was greatest at pump rotation speed of about 2000 r/min. The
fuel control unit was then also connected to the test bench, which allowed the test
fluid flow to be adjusted. This revealed that the leakage rate varied when the flow
was adjusted, being mainly 1 drop per 10 seconds. The leakage did not affect the
operation of the fuel control unit or the fuel flow rate.
The fuel distributor and nozzles were attached to the system. Air bubbles could be
seen especially at the initial stage of the test. Fuel sprays from the nozzles were
even, and no air was detected in them.
The pipe leading to the fuel distributor was then removed, and the other end of the
pipe was inserted into a basin containing test fluid. The test bench was switched
on, but the electric pump was not running. During the whole test, small but clearly
detectable air bubbles were coming from the pipe in the test fluid basin.
1.9
Earlier engine malfunctions and emergency landings on Extra EA300 aircraft
The investigators received a list of emergency landings on EXTRA 300 aircraft
during years 1996–2008 from German accident investigation authorities. Besides
the case now under investigation, there were five incidents on the list.
The list does not indicate the causes of all engine malfunctions, but it mentions
the events leading to an emergency landing. There were three incidents in which
the engine stopped on an aerobatic flight, one in which the engine stopped after
turning the fuel selector valve and one in which the engine stopped during takeoff.
In addition to the incidents listed above, Swiss accident investigation authorities
reported one emergency landing which resulted from engine stoppage due to fuel
exhaustion.
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In the investigators’ opinion, at least a contributing factor to some of these incidents may have been a low fuel amount already when departing for the flight. If
the flight time to the aerobatic practice area is not very long, there may be quite little fuel in the wing tanks since they must be empty when flying aerobatics. After
this, the only usable fuel is 45.5 l in the fuselage tank and the aerobatics tank.
With an average power setting of 75%, the same setting used by pilot in this flight,
this fuel amount means an operating time of 38 minutes.
Finnish Aviation Regulation OPS M1-7, Fuel and oil quantities in flight, requires
that there must be enough fuel in the aircraft tanks to fly for 45 minutes in addition
to the fuel needed for the planned flight time. The regulation does not define
power setting.
2
ANALYSIS
2.1
Probable cause of engine malfunction
From the investigations it could be concluded that the engine and ignition system
were in working order. For this reason, further investigation focused on the fuel
system. Fuselage fuel system was intact, but there was a fuel leak in the engine
fuel pump as a result of seal damage. According to the component manufacturer,
the damage would not have affected the operation of the pump. The manufacturer
did not consider it possible that the pump would convey air to the system either.
There was a minor leak in the fuel distributor valve as well, but it was too small to
affect engine operation. Moreover, experience has shown that the amount of air
(air bubbles) detected in fuel system component testing was so small that it would
not disturb the operation of the fuel control unit. The pressure generated by the
engine-driven fuel pump should also drop below ¼ of the original factory value before it would affect the fuel control unit. The pressure values for the pump under
investigation were as specified in the maintenance manual. Therefore the investigators consider that the engine was in working order, except for the damage
caused in the emergency landing.
The pilot’s description of the engine malfunction clearly indicates that the engine
did not get enough fuel.
The investigators consider it possible that the pilot made a mistake when using
the fuel selector valve. Either a systematic error occurred in the beginning of the
second flight so that the wing tanks were selected when the pilot started aerobatic
flight, or the selection of fuel selector valve position was incomplete (i.e. the valve
remained between two positions). In both cases, the amount of air sucked into the
engine fuel system from almost empty wing tanks could be sufficient to cause a
severe engine malfunction or engine stoppage.
Before departing for the flights, the centre tank had been filled up to 51 l. After the
emergency landing 40 l was remaining. With an average fuel consumption (1.2
l/minute), the fuel quantity used (11 l) is equivalent to a flight time of nine minutes.
According to the logbook entry, the first flight during which the centre tank was
used all the time lasted for six minutes. Therefore the centre tank could only have
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been used for three minutes during the second flight. However, the pilot’s account
gives an impression that the tank would have been used for a longer time.
At the beginning of the first flight, the wing tanks had been 1/4 full of fuel (about 38
l) as shown by the fuel quantity indicator. After emergency landing the tanks had
five litres of fuel in total. The amount of fuel consumed, 33 l, is equivalent to a
flight time of 28 minutes. After the time used for engine run-up, test run and taxiing, the actual flight time remaining was about 21 minutes. The pilot’s account
gives an impression that the tank would have been used for a shorter time.
The combined flight time logged for both flights was 26 minutes. The logbook entries had been rounded to the nearest 1/10 hour. The flight time equals to the
used fuel quantity of 44 litres, considering the possible inaccuracy of fuel quantity
indication and rounding of the flight times.
According to the aircraft operating manual, all the fuel in the wing tanks can be
used and there is no unusable fuel. However, this only applies to straight and level
flight. If wing tanks are used during aerobatic flight, there will be malfunctions in
the engine before the tanks are totally empty. At some stage of the flight, air will
be sucked into the fuel system, which causes engine stoppage. Depending of air
speed propeller may continue rotating as wind mill. If the fuel system is totally or
almost empty, restart will be slower even after switching tanks.
The pilot told that when departing for the flight, he had leaned the mixture by pulling the mixture control lever back about two inches. As the pilot increased power
for taxiing, the engine failed to accelerate but remained at idle and was running
roughly. When the pilot pushed the mixture control fully forward, the engine accelerated normally. During taxiing the pilot leaned the mixture again, but this did not
affect engine performance. In the investigators’ opinion, it is probable that the pilot
leaned the mixture so much at the first time that the amount of fuel was not sufficient to increase power.
2.2
Engine air and oil filter
The EXTRA 300L aircraft type has no regular air filter, but only a simple, rather
coarse net with a mesh size of 1.6 mm. The filtering capacity of the net is not sufficient to prevent any sand and dust, raised from the runway by the propeller, from
entering the engine fuel control unit and further to the cylinders. The dust and
sand wear out the engine very quickly. Cylinder wear increases oil consumption,
which in turn fouls the spark plugs and therefore causes engine malfunctions.
Moreover, contaminants in the air may block the air ducts of the fuel control unit
and cause disturbance in fuel feed. In this case there were noticed dirt in the
spark plugs before engine was reassembled.
A correctly dimensioned and maintained effective air filter limits the maximum
power of the engine only slightly. On the other hand, it brings significant benefits
to the aircraft owner as engine reliability improves and service life increases.
The accident aircraft engine only had a net-type oil filter, which is not as efficient
as the paper element filters currently used in almost every aircraft engine. Since
there is no air filter, dust can be conveyed to the oil through the cylinders. Due to
insufficient filtering capacity of the oil filter, dirty oil accelerates the wear of bearing
surfaces.
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3
CONCLUSIONS
3.1
Findings
1.
The pilot had valid documents as required for the flight duty.
2.
The certificate of airworthiness and the registration certificate were valid.
3.
No technical defect causing the malfunction was found in the engine.
4.
The total flight time for the two flights on the day of the incident was 26 minutes, during which about 44 litres of fuel had been used.
5.
There were only five litres of fuel remaining in the wing tanks after the emergency landing.
6.
About 30 litres of fuel had been used from the wing tanks during the flight.
7.
Only 11 litres of fuel had been used from the centre tank during a flight time
of 26 minutes.
8.
The aircraft fuel consumption at 75% power setting is 1.2 litres per minute.
9.
On aerobatic flights, the amount of usable fuel does not meet the minimum
fuel requirement of Aviation Regulation OPS M1-7, paragraph 2.1.
10. EXTRA 300L aircraft has no air filter.
3.2
Cause of the accident
The cause of the engine malfunction and stoppage could not be conclusively determined. The investigators consider it possible that air was sucked into the engine fuel system. Investigators do not rule out that fuel selector valve was wrongly
or incomplete selected.
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4
SAFETY RECOMMENDATIONS
Since EXTRA 300L aircraft are not equipped with a regular air filter, but only have
a simple, rather coarse net, the filtering capacity is not sufficient to prevent any
sand and dust raised from the runway by the propeller from entering the engine
fuel control unit and further to the cylinders. The contaminants wear out the engine very quickly. Cylinder wear increases oil consumption and fouls the spark
plugs, therefore causing engine malfunctions. Moreover, contaminants in the air
may block the air ducts of the fuel control unit and cause disturbance in fuel feed.
1.
The investigators recommend that the aircraft manufacturer should improve
the air filtration of the engine.
Finnish Aviation Regulation OPS M1-7, Fuel and oil quantities in flight, requires
that there must be enough fuel in the aircraft tanks to fly for 45 minutes in addition
to the fuel needed for the planned flight time. When starting aerobatic flight on an
EXTRA 300L aircraft, the wing tanks must be empty, in which case the only usable fuel is 45.5 l in the fuselage tank and aerobatics tank. With an average power
setting of 75%, this fuel amount means an operating time of 38 minutes. This
amount of fuel is used both for flying the aerobatic manoeuvres and for returning
to the aerodrome.
2.
The investigators recommend that the owners or operators of EXTRA 300
aircraft should apply for an exemption from the minimum fuel requirement
(OPS M1-7, paragraph 6.5) from the Finnish Civil Aviation Authority (Trafi
Aviation).
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Comments on the draft final report on 18 March 2010
Thanks for the opportunity given to EASA to comment on the subject draft final report. The
report is fully comprehensive and well written.
We would like to emphasize, however, some points, hereinafter reported, that you may take
into account in reviewing the draft report. We received them from the aircraft manufacturer.
1. The induction air system was not identified as the reason for the reported engine malfunction. Anyhow, Lycoming suggests only a suitable air cleaner to be incorporated in the
engine induction system. But if an air cleaner is installed, the pressure drop of such an air
cleaner must not exceed 6" H2O. For an acrobatic category airplane, engine power is an
important point. The normal demand is: Keep as much power as you can achieve. So any
manifold pressure loss due to an air cleaner should be avoided.
The background of the existing intake air screen, which is mounted on the outside of the
cowling air intake, is the compliance demonstration to the requirements of §23.1091 (CS23). Alternate air source to the engine is the flow of air into the fuel servo throat via the inside of the cowling (through the defined circular gap between rear end of the cowling intake
and fuel servo) rather than from the outside through the front opening of the air intake of the
cowling. As a result of this, it is important that if the primary flow path is blocked, that the
secondary flow path is available. Without the air intake protection screen in place, anything
that would have blocked the primary air inlet will likely pass into the fuel servo throat, efficiently eliminating both paths of air induction.
This issue was discussed in detail during the validation process of the EA 300 type design
in Canada (Transport Canada; 1994).
2. The EA 300/L type design complies to the requirements of FAR 23 Amdt. 34 (VFR Day).
Fuel is allowed in the wing even when operating the airplane in the acrobatic category fulfilling the 45 min requirement as long as the MTOW for the acrobatic categories are not exceeded. This is important because otherwise, individual EA 300/L airplanes which do not
comply with the most current noise requirements are limited to the acrobatic category could
not ever use the wing fuel tank. BUT: The wing tank must be empty for acrobatic maneuvers because resulting fuel loads are not included in the wing tank load assumptions. That
is why the POH and Placards read: "Wing tank: Must be empty for acrobatics" and not
"Wing tank: Must be empty for the acrobatic category". There are further limitations regarding some acrobatic maneuvers: If you fly inverted there is neither fuel available for 30 min
nor for 45 min. But even so, we still comply to the fuel capacity requirements of FAR 23
(VFR-day) for the acrobatic category.
EASA
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