Interim Report Identification
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Bundesstelle für
Flugunfalluntersuchung
German Federal Bureau of
Aircraft Accident Investigation
Interim Report
Identification
Type of Occurrence: Serious Incident
Date: 13 February 2021
Location: Near Leipzig
Aircraft: Cargo Airplane
Manufacturer: Boeing Company
Type: 757-236 PCF
Injuries to persons: No injuries
Damage: Minor damage to aircraft
Other Damage: None
State File Number: BFU21-0052-EX
Abstract
During initial climb, the main cargo door of the aircraft opened. The flight crew de-
clared emergency and returned to the aerodrome of departure.
Interim Report BFU21-0052-EX
Factual Information
History of the Flight
At 2319 hrs1, after the landing from the previous flight, the airplane taxied to parking
position B424 of Leipzig/Halle Airport. The parking position was under video surveil-
lance. The video showed the following: At 2321 hrs, the previous flight crew opened
the cargo door by about 85%. At 2327 hrs, the flight crew disembarked the airplane.
The ground crew took over. At 2333 hrs, the cargo door was opened farther, inter-
rupted briefly and then opened completely. At 2334 hrs, the ground crew closed the
cargo door completely in one movement. Closing lasted about 45 s. At 2336 hrs, the
door was opened again by about 20% and at 2337 hrs closed again completely. The
cargo remained on board.
At 0320 hrs, the new flight crew boarded the airplane. One person remained in the
crew door and opened the cargo door completely. Opening lasted about 36 s. At
0324 hrs, unloading began. At 0335 hrs, the person using the jump seat boarded the
airplane. The Pilot in Command (PIC) left the airplane at 0338 hrs and conducted the
walk-around check. At 0342 hrs, he returned. At 0409 hrs, unloading was completed.
At 0415 hrs, loading the airplane with new cargo for the flight to Frankfurt/Main Air-
port began and ended at 0441 hrs. At 0443 hrs, one person appeared at the open
crew door and closed the cargo door in one movement. The PIC stated he was the
one closing the cargo door completely, so that all control indications at the control
panel had gone out and the cargo door was flush with the fuselage. According to the
statement of both flight crew members, in the cockpit the cargo door warning light
had also gone out. At 0453 hrs, the airplane was pushed back from the parking posi-
tion. The entire aircraft, wings, fuselage and tail section, were de-iced with Type 4
de-icing fluid. It taxied to runway 26L and at 0531 hrs, took off with Frankfurt/Main
Airport as destination.
During initial climb, the flight crew noticed an unusual pressure change, which was
indicated by a high cabin pressure rate. The flight crew noticed this physically by their
ears popping. As precaution, the cabin altitude mode was switched from AUTO 2 to
AUTO 1. The third person on board, seated on the additional passenger seat be-
tween the cockpit and the upper cargo compartment, referred to permanent air draft
noise during this flight phase. At about 0534 hrs, at about 5,100 ft (AMSL), with an air
1 All times local, unless otherwise stated.
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Interim Report BFU21-0052-EX
speed of about 240 kt, the flight crew heard a loud noise. Because of their perception
and the cockpit indication, they deduced an erroneous opening of the cargo door.
They declared emergency, stopped climbing, began the descent once Munich Radar
had given them clearance and reduced speed. The flight crew decided to return to
Leipzig. Due to the low wind speed on the ground, the airplane returned directly
(Fig. 1) and in agreement with Munich Radar an approach contrary to take-off direc-
tion for the ILS 08R was conducted. Air traffic control had advised a left-hand turn
back to Leipzig/Halle Airport, during which the flight crew noticed that it was difficult
to conduct the change in heading with engaged autopilot. The PIC took over manual
control during a southern heading and realised a significant change in the airplane’s
response to control inputs. During this time the EICAS (Engine Indication and Crew
Alerting System) messages L AFT FUEL PUMP and FUEL CONFIG were displayed
and the fuel quantity indication of the left main tank showed about 1 t less than the
expected quantity, according the co-pilot. The left-hand turn was continued and when
reaching a northern heading, the EICAS messages disappeared and the fuel quantity
indication of the left main tank started to increase again. The flight crew configured
the aircraft for final approach early and shortly before reaching localizer 08R they
switched on first one and then all three autopilots. At 0578 hrs, an automatic landing
was conducted without further problems.
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Interim Report BFU21-0052-EX
Fig. 1: Radar recording of the flight path Source: Air traffic service provider
In agreement with air traffic control, after landing the airplane remained on the run-
way before being towed to apron 4. Figure 2 shows the airplane about 33 min. after
landing with completely open cargo door.
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Interim Report BFU21-0052-EX
Fig. 2: Completely open cargo door after landing Source: Operator:
Personnel Information
The 38-year-old PIC held an Air Transport Pilot License (ATPL(A)) with the type rat-
ing for Boeing B 757/767 issued by the aviation authority of the United Kingdom. He
held a valid class 1 medical certificate. According to the statement of the operator, he
had a total flying experience of 4,000 hours, of which 3,800 hours were flown on Boe-
ing 757. In the last 90 days prior to the occurrence he had flown 68 hours on type.
The 26-year-old co-pilot held a Commercial Pilot Licence (CPL(A)) with the type rat-
ing for Boeing B 757/767 issued by the Swedish aviation authority. She held a valid
class 1 medical certificate. According to the statement of the operator, she had a total
flying experience of 1,100 hours, of which 350 hours were flown on Boeing 757. In
the last 90 days prior to the occurrence she had flown 97 hours on type.
The third person on board was a pilot of another operator who used the jump seat to
fly to Frankfurt/Main Airport. He did not have a type rating for Boeing B 757/767 and
did not participate in the conduct of the flight.
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Interim Report BFU21-0052-EX
Aircraft Information
The aircraft type Boeing 757-236 PCF is an all-metal low-wing airplane with a re-
tractable landing gear in nose wheel configuration. It is equipped with two jet en-
gines. The airplane had a United Kingdom certificate of registration and was operat-
ed by a British freight operator.
In 2011, the airplane with the manufacturer’s serial number 25620 was subject to
conversion from passenger to freight aircraft (Cargo Conversion Number 029) per-
formed by an aero-technical organisation.
The load plan showed a maximum take-off mass of 95,604 kg and a maximum land-
ing mass of 95,254 kg. The calculated actual take-off mass stated in the load sheet
was 76,232 kg. At the time of the incident, it had a total operating time of about
60,790 hours at about 20,210 cycles.
Fig. 3: Three-view-drawing Source: Internet
Design and Function of the Cargo Door
During conversion from passenger to freight aircraft, a cargo door was fitted in the
front left fuselage area. It is 3.40 m wide and 2.18 m high. Its upper end is swivel-
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Interim Report BFU21-0052-EX
mounted to the fuselage with several piano hinges. Two lift actuators, mounted to the
two upper edges, open the cargo door upward and close it downward.
The interlocking mechanism of the cargo door is located at its lower edge and the
cabin floor. A cover protects the mechanism inwards. Eight movable latches, which
are located at the lower part of the door, are hooked into eight latch spools, which are
located in the cabin floor. The interlocking mechanism of the latches is fitted with a
joint connecting rod, which is operated by an eccentric powered by a hydraulic cylin-
der. Each latch is moved with a corresponding rod which is connected with the con-
nection rod via a lever. The latches reach into the spools and once they are in an
over center position the door is closed tight. In this position three drill holes in the
latch mechanism are overlapping and a lock pin is driven through each latch. These
eight lock pins are part of another connecting rod and moved by the respective hy-
draulic cylinder. The ends of the lock pins, which stick out of the drill holes, are colour
marked. This allows the observation of the correct closure from the outside through
eight inspection glasses and a corresponding mirror system.
After the latches are locked and the locking pins are in place a vent door interlock bar
is released so that both vent doors can be closed. These are also powered by a hy-
draulic cylinder.
The main cargo door control panel, located at the left cockpit back wall, allows con-
trol of the main cargo door. The system is switched on by a secured main switch lo-
cated on the control panel. The door is controlled by two spring-loaded switches
(two-hand operation), which spring back to neutral once released. One warning light
and four status lights are mounted to the control panel, which show the individual
state (open or closed) of the cargo door. Once the cargo door is completely closed all
lights are out. Micro switches located in the closing mechanism control the lights.
Each function is secured with two switches and each switch is equipped with two in-
dependent wire connections to the control panel. A separate electrical circuit with
28 V direct current of the aircraft system powers the electro-hydraulic control of the
cargo door. In the cockpit, the cargo door is monitored by a warning light at the left
side of the central instrument panel (P2).
A hydraulic aggregate located on the right side of the lower forward cargo compart-
ment supplies the hydraulic cylinder of the cargo door. This aggregate has no con-
nection with the aircraft hydraulic. The electric motor of the hydraulic pump is sup-
plied by 115 V alternating current of the aircraft system. In case of electric supply
failure, a hand pump allows operation of the hydraulic.
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Interim Report BFU21-0052-EX
When closing the cargo door the lift cylinders are initially supplied with hydraulic
pressure until the door has been lowered completely. On the control panel the light
“NOT CLOSED” is no longer illuminated. Then the system pressure increases and
once 2,000 psi are reached the pressure is passed on to the hydraulic cylinder of the
latches which drives them into the spools and into their over center position. The con-
trol light “NOT LATCHED” is no longer illuminated. Pressure is increased further and
once 2,400 psi are reached it is released through a valve and the eight lock pins are
stuck into the drill holes with the help of the respective hydraulic cylinder. The control
light “NOT LOCKED” is no longer illuminated. The vent doors are closed by the re-
spective cylinder controlled by a valve once the increased pressure reaches
2,800 psi. The control lights “VENT DOOR OPEN“ and „MAIN CARGO DOOR“ are
no longer illuminated and neither is the warning light “MAIN CARGO DOOR” in the
cockpit. Once all lights are out, the cargo door is completely closed and locked.
Operation of the cargo door was done from the control panel. It was performed by the
flight crew or by trained ground personnel.
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Interim Report BFU21-0052-EX
Fig. 4: Main Cargo door Source: Manufacturer
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Cargo Compartment
The cabin floor was equipped with mountings for airfreight containers. The cabin
could hold a maximum of 15 containers. At the day of the occurrence, 11 containers
were fastened to the positions 1 and 6 to 15. The positions 2 to 5, which are close to
the cargo door, remained free.
Fig. 5: Cargo compartments Source: Operator
Meteorological Information
The aviation routine weather report (METAR) of 0420 UTC of Leipzig/Halle Airport
described the following weather conditions:
Wind: 270°/3 kt
Visibility: RVR RWY 26L 500 m (downward tendency)
Cloud: Patches of fog, no significant cloud
Temperature: -15°C
Dewpoint: -17°C
QNH: 1,038 hPa
During the time the aircraft was at the parking position, freezing fog, which changed
to patches of fog at about 0350 UTC, prevailed.
Aids to Navigation
The flight was conducted under instrument flight rules. During the approach and land-
ing the ILS of runway 08 was used.
The air navigation service provider provided the BFU with the radar recording of the
flight for evaluation purposes (Fig. 1).
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Radio Communications
Radio communications between the flight crew and the air traffic control unit were
recorded. Transcripts of the recordings were made available to the BFU.
Aerodrome Information
Leipzig/Halle Airport had two concrete runways. They have the markings 08R/26L
and 08L/26R; each was 3,600 m long and 60 and 45 m wide, respectively. The air-
port had five concrete aprons. The parking position on which the freighter was parked
prior to departure is located at apron 4.
Flight Recorder
The Flight Data Recorder (FDR), Honeywell SSFDR-12311, and the Cockpit Voice
Recorder (CVR), Honeywell SSCVR-0829, were available for read-out by the BFU.
They could be read-out without any problems.
FDR Graph
Figure 6 shows the following parameters of the entire flight:
Pressure Altitude in [ft], Computed Airspeed in [kt], Vertical Speed in [ft/min], Head-
ing Magnetic in [°], Roll Angle in [°], Left Aileron Position in [°], Right Aileron Position
in [°], Lateral Acceleration in [g], Vertical Acceleration in [g], Angle of Attack in [°] and
A/P-L, A/P-C and A/P-R (engaged or disengaged).
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Fig. 6: FDR data of the entire flight Source: BFU
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The graph in Figure 7 shows the time period of 2.5 min. prior to and about 6 min. af-
ter the cargo door opened with the same parameters depicted in Figure 6. After the
flaps were retracted and the airplane had accelerated to about 240 kt, at
0434:29 UTC, at about 5,100 ft (AMSL), lateral acceleration suddenly increased from
0 to +0.1 g and heading changed by 5° to the right. At the time, the ambient noise
level on the CVR recording increased considerably. In this phase, the autopilot A/P-C
was engaged. Initially the airplane responded with a slight roll angle to the right,
which was compensated by aileron deflections resulting in a left bank angle of 5° to
8°. Until 0435:19 UTC, heading changed back to the originally selected. At
0434:37 UTC, the crew pushed the altitude HOLD switch on the mode control panel.
The airplane levelled off and at 0434:49 UTC began to descend.
After the heading back to Leipzig/Halle Airport was selected at 0435:23 UTC, lateral
acceleration increased to about 0.15 g and the airplane initially began to change
heading. Figure 7 shows that at 0437:29 UTC the heading of about 160° does not re-
ally change any more. At 0438:25 UTC, A/P-C was disengaged (Fig. 7) and then the
aircraft controlled manually. Afterwards the FDR had recorded larger aileron deflec-
tions and a temporary increase in left roll angle to about 37°, among other things.
Another change of lateral acceleration to about 0.25 g occurred. The change of head-
ing increased again and the left-hand turn was continued.
In addition to the lateral acceleration and the roll angle, the graph in Figure 8 also
shows fuel and engine parameters.
Before the A/P-C was disengaged at 0438:10 UTC, the left main tank indication
showed a fuel quantity of 2,703 kg and the right of 2,993 kg (Fig. 8). At 0439:16 UTC,
this difference of 290 kg changed to 792 kg, 25 s after the lateral acceleration had in-
creased to about 0.25 g.
The EICAS message L AFT FUEL PUMP was triggered at 0438:57 UTC, at about
the same time as the lateral acceleration changed to about 0.25 g and disappeared
at 0439:29 UTC. At the time, lateral acceleration was about 0.05 g. At 0439:29 UTC,
the EICAS message FUEL CONFIG was triggered, 13 s after the difference between
both main tanks had been 792 kg.
At 0439:24 UTC, at a left roll angle of 37°, EPR (Engine Pressure Ratio) of the left
engine decreased in comparison to the right to 1,025 (Fig. 8). At the time, the Thrust
Lever Angle (TLA) of both engines was about the same.
At 0439:39 UTC, 15 s later, both engines showed about the same EPR values again.
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Fig. 7: FDR data between 2.5 min prior and 6 min after the cargo door opened Source: BFU
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Fig. 8: Engine and Fuel Parameters Source: BFU
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Findings on the Aircraft
After landing, the airplane remained on the runway. The engines were shut down.
Fire brigade and ground personnel checked the airplane from the outside for hazard
sources. They noticed the missing interior lining of the door. The photo (Fig. 9) which
had been taken on the runway shows that the vent doors are almost closed. The
latches show a not completely open position (Fig. 10). Then the airplane was towed
to the apron. More photos were taken. These show that almost all control lights on
the control panel of the cargo door are illuminated, among other things. One photo,
taken of the cockpit, shows that the warning light MAIN CARGO DOOR is illuminat-
ed.
The crew disembarked and the technicians took over. Initially, the airplane was
towed to a nearby hangar. Due to the high demand of this hangar it was decided to
tow the airplane to a less frequented one. As safety action and to meet the require-
ments of the cargo door manufacturer the door was lowered prior to towing the air-
plane again. The lift cylinders were used to accomplish this. The door was secured
with ropes and a crane to prevent it from falling off.
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Vent Doors
Fig. 9: Position of the vent doors after the landing Source: Operator
Fig. 10: Position of the latches after the landing Source: Operator
On 15 February 2021, a Borescope inspection on the intermediate and high pressure
compressor of the left engine was performed and showed no findings.
Contact with the cargo door manufacturer was established and two advisers request-
ed for the examination of the cargo door. Due to Covid-19 regulations the organisa-
tion took a few days’ time. The examination was continued on 20 February 2021. The
left wing leading edge of the airplane, between fuselage and engine pylon, showed
some scratch marks. The rest of the examination addressed the cargo door.
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It was open by about 40 cm and was secured with a traverse and a suspension crane
(Fig. 11). The vent doors were open.
Fig. 11: Status on 20 February 2021 Source: BFU
The examination of the cargo door revealed that the piano hinges, which connected
the cargo door with the fuselage, showed chipped paint. The lift cylinder hinges and
the parallel running bell-crank levers were distorted. The inner lining of the cargo
door was missing.
The casing of the forward wiring harness, which is one of two harnesses connecting
the micro-switches with the control panel, had been pulled off in the area of the plug
at the door. The aft wiring harness had been torn off.
One of the two flexible hydraulic lines, connecting the cargo door with the hydraulic
system on the fuselage side, showed a leak. Hydraulic fluid stuck to the inside of the
door.
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The inside of the cargo door was also inspected for traces of de-icing fluid. No resi-
due or traces were found.
The examination of the locking system revealed that the lock pins did not go into their
final position through the drill holes in the latches. The connecting rod of the lock pins
showed no damage. The tips of the lock pins showed slight scratch marks. The
latches were not completely open. The respective connecting rod did not show any
damage. The actuator of the latches was not completely extended. The screw heads
of the individual hooks in the area of the drill holes and the latch elements (Fig. 12)
showed damage in the form of grooves.
Damage
Fig. 12: Damage at the latches Source: Operator
During a later examination, the status of the latches described above was recon-
structed and revealed that the door could be pushed open manually. The latches slid
across the latch spools on the floor. The upper surface of the spools showed scratch
marks.
It was attempted to operate the locking mechanism and the vent doors manually with
the hydraulic system’s hand pump. The hydraulic-mechanical system revealed an er-
ror in its motion sequence. The hydraulic system was examined in more detail and air
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in the system detected. It cannot be ruled out that air had been in the hydraulic sys-
tem before the leakage described above occurred.
Due to the design of the cargo door, which consists of two main components, the hy-
draulic-mechanical moving and locking mechanism and the electrical control circuit,
two possible incident scenarios are being investigated.
Initially, the hydraulic and the mechanism, as described above, were considered.
Then the electrical system was examined. So far, the examinations of the electrical
system have not revealed any irregularities.
The examianitons of both components are still ongoing.
Fire
There was no fire.
Additional Information
On 6 December 2014, a similar incident occurred at Magadan, Russia. The incident
involved a Boeing 757-200 PCF where the main cargo door opened completely dur-
ing initial climb. The airplane returned to the aerodrome of departure and landed
without further incidents. At the time, the temperature was -14°C and slight snowfall
prevailed.
Safety Recommendations
After the incident, the operator of the aircraft issued a safety action for their entire
757-236 PCF fleet. Accordingly, after closing the cargo door, the latches have to be
checked from the outside through the eight inspection glasses. Attention must be
paid to the latches being correctly locked and the locking pins being in their respec-
tive drill holes. The flight crews are advised to pay attention to the cargo door indica-
tions in the airplane. This should ensure that prior to the flight the cargo door is com-
pletely closed and locked. Instructed personnel conduct these checks.
Investigator in charge: Nehmsch
Field Investigation: Nehmsch, Bielfeldt
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This investigation is conducted in accordance with the regulation (EU) No. 996/2010
of the European Parliament and of the Council of 20 October 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 (Flugunfall-Untersuchungs-Gesetz - FlUUG) of 26 August 1998.
The sole objective of the investigation is to prevent future accidents and incidents. The
investigation does not seek to ascertain blame or apportion legal liability for any claims
that may arise.
This document is a translation of the German Investigation Report. Although every effort
was made for the translation to be accurate, in the event of any discrepancies the original
German document is the authentic version.
Published by:
Bundesstelle für
Flugunfalluntersuchung
Hermann-Blenk-Str. 16
38108 Braunschweig
Phone +49 531 35 48 - 0
Fax +49 531 35 48 - 246
Mail box@bfu-web.de
Internet www.bfu-web.de
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