12-AX002 UB EN V04 DN

Bundesstelle fürFlugunfalluntersuchung German Federal Bureau of Aircraft Accident Investigation

Investigation Report The Investigation Report was written in accordance with para 18 Law Relating to the

Investigation into Accidents and Incidents Associated with the Operation of Civil Air-

craft stating facts only.

Identification

Type of Occurrence: Accident

Date: 17 May 2012

Location: Munich

Aircraft: Transport aircraft

Manufacturer / Model: Avion de Transport Regional / ATR 72-500

Injuries to Persons: 6 persons suffered minor injuries

Damage: Aircraft substantially damaged

Other Damage: Ground measuring equipment damaged

Crop damage

State File Number: BFU AX002-12

Investigation Report BFU AX002-12

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Factual Information

History of the Flight

At 1335 hrs1, the transport aircraft took off from runway 26L of Munich Airport with 4

crew members and 58 passengers on board; destination airport was Venice, Italy.

After about 9 minutes of flight time, at 1344 hrs, a flight attendant informed the pilots

that smoke had developed in the cabin. She said that the smoke had some electrical

cause. The aircraft was approximately at Flight Level (FL) 120. The climb speed was

about 170 kt. The Pilot in Command (PIC) was also Pilot Flying (PF).

At 1345 hrs, the co-pilot reported via radio: “[…] we have smoke on board, we can-

cel, coming back […].” According to the CVR, the pilots donned their oxygen masks

and then the controller confirmed the report.

At 1346 hrs, the climb was aborted and the aircraft levelled off at FL 146. According

to the FDR, airspeed increased and at 1348 hrs had reached about 220 kt (Appendix,

Fig. 1). The co-pilot informed the controller that the aircraft would return to Munich.

Then the pilots completed the Emergency Checklist Electrical Smoke (1.05A) (Ap-

pendix, Fig. 2). One item on the list was put DC BTC push button in ISOL, meaning

disconnect, which occurred at about 1347 hrs.

At 1348 hrs, the controller instructed the crew to descend to FL 110. Then engine

power was reduced and the descent initiated. Subsequently, Master Caution and En-

gine 2 Fire warnings were generated. The flight crew triggered the first fire extin-

guisher bottle. This extinguished the fire in the right engine and the pilots shut down

the engine. Subsequently, the PIC informed the cabin crew and the passengers

about the event. The co-pilot informed the controller that due to fire they had shut

down engine No. 2. He also enquired about an emergency landing and confirmed the

continuation of the descent. At 1350 hrs, the pilots removed their oxygen masks. One

minute later they began to complete the Emergency Checklist In Flight ENG Fire or

Severe Mechanical Damage (1.02) (Appendix, Fig. 3).

At 1352 hrs, frequency was changed to approach control. The aircraft was cleared for

descent to 5,000 ft AMSL. Afterwards the pilots completed the Following Failures

Power Plant Checklist Single ENG Operation (2.04) (Appendix, Fig. 4). The PIC dis-

1 All times local, unless otherwise stated.


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cussed the impending evacuation with the flight attendant. After this conversation the

Normal Procedures Checklists Descent and Approach were completed.

At 1355 hrs, frequency was changed to final approach control. The PIC explained to

the controller the situation on board. He informed him about the impending evacua-

tion after the landing and requested support by the airport fire brigade. The controller

confirmed this.

At 1356 hrs, the PIC asked about the situation in the cabin. The flight attendant con-

firmed that there was still smoke in the cabin and again expressed her assumption

that an electrical problem caused it. The PIC disagreed due to the problem with en-

gine No. 2. In addition, they again discussed the impending evacuation. Then PIC

and co-pilot discussed in which area of the runway the evacuation should take place.

The aircraft was still in descent and the controller guided it to the Instrument Landing

System (ILS) of runway 26L.

Sequence of events, according to FDR and CVR data:

1359 hrs: The flight attendant reports that the cabin was prepared for

emergency landing.

1400 hrs: The final approach controller transmits the landing clearance

of the tower and the wind data, 5 kt from 240°.

1401:06 hrs: The flaps are extended to 15°, indicated airspeed is 176 kt,

the aircraft is at 2,600 ft AMSL.

1401:16 hrs: The landing gear is extended.

1401:22 hrs: The TLU Fault single chime is generated.

1401:33 hrs: The autopilot is disengaged; speed is 160 KIAS, altitude

2,150 ft AMSL.

1401:36 hrs: Flaps are extended to 30°.

1401:46 hrs: The pilots complete the Normal Procedures Checklist Final.

Excerpt CVR Recording:

Pilot Non Flying (PNF) Pilot Flying (PF)

Landing Gear Is down, three green

Flaps 30 / 30


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TLU green light On

Power engine selec Take-off

LA speed Off, normal speed

Rudder trim Neutral

Final Checklist is complete, cleared to

land

Well

1402:11 hrs: The PIC asks if the Yaw Damper is switched off; the co-pilot

confirms this.

1402:17hrs: The PIC realises that the rudder is stuck and instructs the co-

pilot to help by pushing the rudder pedal with his left foot

(1,650 ft AMSL, ground speed about 120 kt). The co-pilot con-

firms that he would facilitate the rudder input.

1403hrs: The power lever is retracted by about 20%, the engine torque

drops to 0%.

1403:03 hrs: Shortly before touch-down the airplane begins to yaw to the

left. At the beginning it has a direction of 280°. The rudder is

fully deflected to the left. This means full deflection 5° since

the rudder limitation was in High Speed Mode. After the be-

ginning of the yaw movement the rudder is deflected right to

the mechanical stop (5°). Prior to touch-down, roll angle is 3-

5° to the left and after touch-down drops to 0°.

1403:05 hrs: The aircraft touches down on runway 26L with a speed of ap-

proximately 98 kt.

1403:07 hrs: The right propeller switches to Low Pitch, the engine torque

increases to 30%. The yaw movement of the airplane to the

left continues until a heading of 200° is reached. Therefore,

the ground traces describe a drawn-out left-hand turn.

1403:15 hrs: The airplane veers off the runway with a ground speed of ap-

proximately 73 kt.

1403:17 hrs: The airplane collides with the antenna of the visual range me-

ter.


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At about 1403:20 hrs: The nose landing gear collapses at a bump and the aircraft

comes to a stop in the grass after about 300 m.

Since the left engine could not be shut down with the usual procedure the emergency

procedure for engine fire was used, according to the pilots. At 1404 hrs, the PIC or-

dered the evacuation via the doors at the right side. All 58 passengers and the 4

crew members were evacuated via these 2 emergency exits. Six passengers suf-

fered minor injuries.

Personnel Information

Pilot in Command

The 42-year-old PIC of the ATR 72 held an Airline Transport Pilot's License

(ATPL(A)), initially issued on 19 November 2009 by the Italian civil aviation authority

in accordance with JAA regulation. The license listed the type ratings for ATR 42 and

72 and ME, MP and IR valid until 28 February 2013.

His class 1 medical certificate was valid until 23 August 2012 without restrictions.

The PIC had a total flying experience of 7,804 hours and 30 minutes. His flying expe-

rience on type was 5,559 hours and 18 minutes. In the last 90 days he had flown

145 hours and 48 minutes and in the last 30 days 49 hours and 50 minutes. In the

last 24 hours prior to the accident flight he had had a duty time of 8 hours and

43 minutes, of which he had flown 4 hours and 54 minutes.

Co-pilot

The 35-year-old co-pilot held an ATPL(A). The licence was initially issued by the Ital-

ian civil aviation authority on 21 January 2005 in accordance with JAA regulation.

The license listed the type ratings for ATR 42 and 72 and ME, MP and IR valid until

22 November 2012.

His class 1 medical certificate was valid until 15 April 2013 without restrictions.

He had a total flying experience of 4,477 hours and 9 minutes. His flying experience

on the ATR 72 was 1,677 hours and 9 minutes. In the last 90 days he had flown

140 hours and 39 minutes and in the last 30 days 70 hours and 42 minutes. In the

last 24 hours prior to the accident flight he had had a duty time of 8 hours and 43

minutes, of which he had flown 4 hours and 54 minutes.


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Aircraft Information

The transport aircraft ATR 72-500 is a high-wing airplane in all-metal construction

with a retractable tricycle nose wheel landing gear. It is equipped with two turbo-prop

engines.

Manufacturer: ATR-GIE Avions de Transport Regional

Type: ATR 72-212A

Manufacturer's

Serial Number (MSN): 664

Year of manufacture: 17 April 2001

MTOM: 22,500 kg

Total airframe hours: 20,333 hours and 20,450 cycles

Engine: Pratt & Whitney PW 127 F

Propeller: Hamilton Standard 568F

The aircraft had a valid Italian certificate of registration and was operated by an Ital-

ian operator.

Meteorological Information

On the day of the occurrence visual meteorological conditions prevailed at Munich

Airport. Wind velocity was 240°, 5 kt. Ground visibility was more than 10 km.

Aids to Navigation

For the approach and landing the airport’s instrument landing system was used.

Radio Communications

The air navigation service provider recorded the radio communications. The tran-

script was made available to the BFU, which aided the compilation of the CVR re-

cording transcript and the time levelling with the course of the flight.


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Aerodrome Information

Munich Airport (EDDM) had two parallel concrete runways. Both runways had the di-

rection 082 /262° and each a length of 4,000 m and a width of 60 m. The 3 aprons

and the taxiways also had concrete pavements.

Flight Recorder

The airplane was equipped with a Flight Data Recorder (FDR) Fairchild FA2100 and

a L3 Cockpit Voice Recorder (CVR). The recorders have been made available to the

BFU for the investigation.

The recordings were used for the reconstruction of the course of the flight and the

chronology. The report includes excerpts and graphs.

Wreckage and Impact Information

The tracks the landing gear had left began about 1,150 m after the beginning of run-

way 26L right of the centre line. They ran in a wide arch to the left towards the south

airport fence (Appendix, Fig. 5).

At about 1,290 m after the threshold the airplane left the runway. The track crossed

the westernmost antenna of the RVR system. The antenna, including the control box,

was torn out of the ground. Fracture pieces of the nose landing gear doors were

found behind the antenna. The track the nose landing gear had left in the grass

showed that the turf was damaged in six different places at varying distances. The

airplane came to a stop 61.5 m in front of the airport fence; the airplane nose pointed

toward 205°.

When the BFU arrived at the site both front emergency exits, both aft doors and the

cargo compartment door were open. The aircraft nose was damaged. Both main

landing gears were extended. The nose landing gear was pushed inside the wheel

bay which was filled with grass and soil. The fuselage bottom surface was dented in

the area behind the nose landing gear bay. The flaps were extended to 30° (Appen-

dix, Fig. 6).

Both propellers were feathered. The left propeller could be turned manually. The right

propeller could not be turned manually. The lower part of the right engine cowling

was covered with oil. The upper aft part of the engine cowling showed traces of


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smoke. Once the cowling was opened traces of fire, and in the aft part of the engine,

a few broken pipes became visible.

The oxygen masks in the cockpit had been removed from their storage containers.

The power levers located in the middle console could not be moved.

The right engine was removed for further examination.

Examination of the Rudder Control

The rudder system was examined once the airplane had been recovered, moved to a

hangar and jacked up. It was determined that the rudder pedals could only be moved

to a limited extent. The Travel Limiter Unit (TLU), which limits the deflection of the

rudder, was in High Speed Mode. The control rods of the drive were retracted. After

the TLU had been separated mechanically, the rudder pedals were free and the rud-

der could be moved freely to the suspension points.

After the TLU had been checked mechanically, it was checked electrically by use of

the aircraft battery. The initial situation was as follows: The TLU Fault indication on

the instrument overhead panel was illuminated. There was no LO SPD2 indication

and the Bus Tie Contactor (BTC), the push button connecting the two bus bars, was

in the position Disconnect. After the TLU push button had been switch manually to

Low Speed, the LO SPD indication on the instrument panel became green. The TLU

Fault indication went out and the TLU drive extended allowing full rudder deflection.

After the TLU push button had been switched manually to High Speed the LO SPD

indication went out, after about 25 s the TLU Fault indication was illuminated and the

TLU drive retracted.

The aircraft was then connected to a ground power unit. The initial situation was as

follows: The TLU push button was in the Auto position, the BTC push button was in

the position Disconnect, the LO SPD indication was off and the Fault indication illu-

minated. The FLT-CTL3 indication at the Caution Advisory Panel (CAP) was not illu-

minated. The TLU drive was in high speed. Then the BTC push button was put in po-

sition Connect, which connected the two bus bars. The following situation presented

itself: On the instrument panel the LO-SPD indication was green and the fault indica-

tion went out. The TLU power unit moved to low speed mode.

2 LO SPD: Low Speed 3 FLT CTL: Flight Control


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Examination of the Engine

The right engine, which had lost power, was removed and sent to the manufacturer.

Under supervision of the Transportation Safety Board of Canada (TSB), the engine

manufacturer conducted further examinations of the engine. This examination

showed that the turbine blade fracture at the second stage of the power turbine had

caused the engine failure. The fracture and metallurgical analyses showed that the

turbine blade had fractured above the root platform in the area of the blade due to fa-

tigue fracture with subsequent residual fracture caused by tensile overload. The frac-

tured blade caused damage on other turbine blades.

The crack originated below the surface in the area of the leading edge of the blade.

Since the fracture surface did not show any defects which could have given any indi-

cation regarding the crack origin, a metallographic cross section was made from the

area of below the fracture surface. It showed a vein-like planar inclusion with high

portions of Aluminium (Al), Chrome (Cr), and Titan (Ti), which highly likely initiated

the crack origin.

Subsequently, one ventilation pipe and the pressure/ventilation pipes of bearing

housings Nos. 6 and 7 fractured causing static pressure fluctuations in the accessory

gearbox and internal/external oil leakage. The secondary air system was contami-

nated with oil.

The other engine damage was secondary damage.

Fire

During the flight a fire in engine No 2 occurred. It was extinguished by means of the

first fire extinguisher bottle.

Additional Information

Interview of the Cockpit Crew

The 2 pilots were invited to Braunschweig to listen to the CVR recordings and be in-

terviewed. During the interview the item from the Normal Procedures Checklist Final

TLU green light On

was discussed. The pilots were asked which indication regarding the TLU they had

observed. The PIC stated that he could not remember the indication TLU green light,


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but he did not have any indication on the CAP. He also said, that in that moment it

was not clear to him that under the conditions the CAP had not been supplied with

power.

The co-pilot stated that at the time he had read the checklist and could not remember

the indication.

Structure and Function of the Travel Limiter Unit

The task of the TLU is to limit the rudder deflection at an indicated airspeed of more

than 185 kt. This equals the maximum speed if the flaps are extended by 15°. The

system has 2 positions. Full Authority Position means complete rudder deflection.

Reduced Authority Position means rudder deflection is limited to both sides to about

5°.

The limitation occurred in the area of the rudder linkage in the fuselage tail. An elec-

trically operated actuator drove a lever fitted with a roller into the V-shaped dent of a

cam disc. The roller, which then was in the dent of the cam disc, was the mechanical

stop which limited rudder deflection. In normal operation, the actuator drive was pro-

vided with +28 V from the main bus bar 2 28VDC. The Emergency bus bar VDC pro-

vided +28 V in case of emergency.

In normal operation, the actuator drove the roller lever automatically into the V-

shaped dent of the cam disc (actuator retraction). Once speed fell below 180 kt the

actuator moved back into its original position allowing full rudder deflection. Each ac-

tion took about 15 seconds. In provision mode, where the actuator is operated via the

3-positions switch in the panel 25VU (Appendix, Fig. 7), it took about 30 seconds.

The control and indication of the TLU occurred at different places in the cockpit (Ap-

pendix, Fig. 7). On the panel 25VU, which is located at the left overhead panel above

the PIC, there was a Fault Indication and a push button with 3 positions: Low Speed,

Auto, High Speed. The push button was covered and its medium position (Auto) se-

cured. On the panel 404VU, as part of the central instrument panel in front of the pi-

lots, the LO-SPD indication was located to the right next to the engine indications. It

was green if the TLU was in the Full Authority position.

The TLU was controlled by comparison of the true position of the actuator and the

speed in relation to the maximum speed at 15° flap deflection. The following warn-

ings were triggered if conflicts in the reference values occurred: Master Caution, FLT

CTL indication on the CAP and a Single Chime. The Single Chime was triggered

about 25 s after speed fell below 180 kt.


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The Master Caution indication was located on the left instrument panel (PIC) be-

tween the altimeter and the stand-by horizon and on the right instrument panel (co-

pilot) above the clock. The CAP was located below the stand-by horizon (Appendix,

Fig. 7 and 8). The CAP indication occurred whenever a fault emerged in the respec-

tive system. Conversely, this means if no indications on the CAP are illuminated all

systems function properly. The DC BUS 2 supplied the CAP with power. It in turn

was supplied by the DC GEN 2 which was powered by the right engine.

Direct Current Production and Distribution

The direct current was generated by 2 independent starter generators, which were

powered by the respective engine. The direct current from the generator of the left

engine supplied power for the DC BUS 1 and the one from the right engine DC BUS

2. Voltage was 28 V.

BTC Push Button

Via the push button the two bus bars were connected. In normal operation, the push

button is free and via a control unit connection or disconnection is automatically se-

lected depending on need. If the BTC push button is pushed both bus bars are dis-

connected. The indication ISOL (Isolation) on the push button indicates the discon-

nection.

Air Condition

The air condition system consisted of 2 units which were powered by the engines.

The air condition system regulated the air airflow and the temperature in the cabin

and the cockpit. The left unit supplied the cockpit and the cabin and the right just the

cabin.

Air Traffic Control

After the crew had declared emergency and said they had decided to return to Mu-

nich, 7 minutes passed until landing. During this time period the air navigation service

provider had 29 radio contacts with the crew and 2 changes of frequency occurred; in

total 3 air traffic control units were involved.

Normal Procedures Checklist

The item “TLU green light” of the Normal Procedures Checklist Final of the operator

(Appendix, Fig. 9) stated:


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TLU green light On

The same item on the aircraft manufacturer’s Normal Procedures Checklist Before

Landing showed the following (Appendix, Fig. 10):

TLU green light Check Low Speed

Investigator in charge: Nehmsch

Assistance: Karge, Ritschel, Hempelmann

Field Investigation: Nehmsch, Berndt

Braunschweig 10 February 2020


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Appendices

Fig. 1: FDR data flight path Sou


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Fig. 2: Check List 1.05A Source: Manufacturer

Fig. 3: Check List 1.02 Source: Operator


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Fig. 4: Check List 2.04 Source: Manufacturer


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Fig 5: Accident site overview Source: Police HUST, Munich, Bavaria


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Fig 6: Accident site Source: BFU


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Fig. 7: Travel Limitation operation and indications Source: Manufacturer


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Fig. 8: Instrument panel Source: BFU

Fig. 9: Check List FINAL Source: Operator


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Fig. 10: Check List BEFORE LANDING Source: Manufacturer


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This investigation was conducted in accordance with the regulation (EU)

No. 996/2010 of the European Parliament and of the Council of 20 Octo-

ber 2010 on the investigation and prevention of accidents and incidents in

civil aviation and the Federal German Law relating to the investigation of

accidents and incidents associated with the operation of civil aircraft (Flu-

gunfall-Untersuchungs-Gesetz - FlUUG) of 26 August 1998.

According to the law the sole objective of the investigation shall be the

prevention of future accidents and incidents. It is not the purpose of this

activity to assign blame or liability or to establish claims.

Published by: German Federal Bureau of Aircraft Accident Investigation Hermann-Blenk-Str. 16 38108 Braunschweig Phone ++49 531 3548-0 Fax ++49 531 3548-246 Mail [email protected] Internet www.bfu-web.de

12-AX002 UB EN V04 DN

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