11
1 INTRODUCTION
The potential spill of fuel and other harmful substances
from the plane that sank into Lake Gružan could have
caused a huge ecological disaster, jeopardizing the
water supply of thousands of residents of the nearby
towns. Solving the problem required a quick and
efficient response, namely the engagement of highly
trained personnel from various fields, but as well as the
use of appropriate specific equipment. The case study
describes a modular approach to crisis management
and provides the original solutions that were applied
during the deployment of Serbian Armed Forces units
in resolving such a specific task
The second chapter of the paper presents the basic
information about the event — when it occurred, the
cause of the crash and a description of the location
where the aircraft sank. The third chapter describes the
operation planning, the preparation and organization
of forces, the use of diving and pontoon units
(Applying various techniques and procedures), as well
as the process of disengagement from the operation
zone. Finally, the fourth chapter and the conclusion
provide a brief summary in the form of lessons learned,
namely the positive and negative experiences gained
during of this operation.
The Recovery of Sunken Object from a Lake – Study
Case
S. Bajrami, S. Soskic, I. Petrovic & M. Kresojevic
Military Academy, Belgrade, Serbia
ABSTRACT: The recovery of sunken objects from the sea, rivers and lakes is a complex and dynamic activity
where actors meet up with numerous problems and challenges such as: unpredictability, quick response,
unavailability of valid information, engagement huge number of subjects and a high risk of activity. The execution
of such and similar tasks requires: multidisciplinary approach, adequate selection of personnel and resources,
successful deployment of forces to inapproachable terrain, efficiency locating of sunken objects and original
solutions. The primary aim of this paper is to highlight the key elements of search and rescue operation through
the form of a case study which is based on detailed analysis event of the recovery of a sunken fighter jet from the
"Gruža" Lake in the Republic of Serbia. The methods that will be applied in the preparation of this work will be
based on fundamental scientific methods in order to provide valid and comprehensive data about the event. For
instance, content analysis of command documents will provide key information such as: forces, resources, time
of engagement, organization, etc., while the interview method will gather date from direct participants regarding
to the problems, challenges and specific solutions which were applied in the field. The expected result of the
research is that, through systematizing experience and learned lessons, generate paradigm of good practice which
can be use like solution for solving future similar tasks.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 20
Number 1
March 2026
DOI: 10.12716/1001.20.01.02
12
2 BASIC INFORMATION ABOUT THE INCIDENT
On June 3, 2010, at 11:17 hours, four J-22 Orao fighter
jets (Figure 1) took off from the Lađevci Airport near
Kraljevo. They were practicing low-altitude flight
mission. The formation followed the route Lađevci–
Paraćin–Ćuprija–Batočina–Knić–Lađevci. After
completing the mission, during landing, the pilot was
forced to eject due to the inability to deploy the landing
gear. The landing gear was initially attempted to be
deployed via the hydraulic system and then manually.
As a final attempt the pilot even tried to lightly touch
the runway with the other wheels in an attempt to use
inertial forces to release the stuck wheel.
Figure 1. Fighter jet type J-22 „Eagle”
Due to a low amount of fuel, it was decided to fly to
the nearby Gruža Lake and abandon the aircraft over
it, in order to avoid potential casualties and damage on
the ground. At around 12:00 hours, the pilot ejected
from the aircraft at an altitude of 500 to 700 meters, and
the aircraft crashed into the lake.
Gruža Lake (Figure 2), one of the largest reservoirs
in central Serbia, supplies water to the city of
Kragujevac and the municipality of Knić. This artificial
lake was formed in 1983 by damming the Gruža River
and is located in the municipality of Knić. With a
capacity of 64.5 million cubic meters and an area of 900
hectares, the lake has an average depth of 6.5 meters at
maximum water level, while the maximum depth
reaches 35 meters [1]. In its northern part, the lake is
between 1,000 and 2,000 meters wide, while in the
southern part (toward the dam), it narrows to between
100 and 500 meters. At maximum water level, the
shoreline is 42 kilometres long.
Figure 2. Gruzansko lake
Based on the presented data about the lake, two
basic conclusions can be drawn. First, it is a massive
reservoir of drinking water that supplies a large
number of residents in the surrounding areas. Second,
due to the lake's large surface area, locating sunken
objects presents a very challenging task. Therefore,
besides the usual challenges typical of search and
recovery operations (such as a large search area),
participants also faced a potential crisis situation
(contamination of drinking water). In order to prevent
further problems caused by fuel and oil leakage, the
speed of the intervention was of critical importance,
which further complicated the search and recovery
operation. In this context, interviewing eyewitnesses
proved to be very important, аlthough their statements
about the crash site were contradictory. However, by
cross-referencing all collected data, the search area was
reduced from 900 to 92 hectares. This information later
turned out to be crucial for the rapid recovery of the
aircraft and for preventing chemical pollution of the
reservoir.
3 OVERVIEW OF THE SEARCH AND RECOVERY
OPERATION OF THE FIGHTER JET FROM THE
LAKE
There are various criteria for classifying military
operations. For example, based on the nature of the
task to be performed, operations are divided into
combat and non-combat operations. In combat
operations, the primary goal is to impose one's will on
the enemy through the use of armed force, unlike non-
combat operations, where the desired end state is
achieved through non-combat activities. However,
regardless of the differences between combat and non-
combat operations, every military operation consists of
three basic phases: preparation, execution and
stabilization or disengagement of forces [2].
The operation in question is classified as a non-
combat operation, within which these three basic
phases can also be identified.
3.1 Preparation Phase of the Operation
The preparation phase of the operation involves the
activities of commands and units conducted
immediately prior to the execution phase, with the
main goal of building and maintaining a high level of
operational capability required for the successful
execution of the upcoming operation. Purposeful and
timely preparations are intended to ensure the effective
use of units in accordance with a unified plan and
under unified command for the entire duration of the
operation [3].
The conditions under which the preparation phase
is carried out depend on many factors such as: the
condition and availability of equipment, the amount of
time available for preparation, availability and training
level of personnel, as well as the quality of information
available to the command during both preparation and
execution phase of the operation.
To avoid or mitigate potential consequences caused
by the aforementioned factors, the preparation phase
typically includes key activities such as: operation
planning, organization of forces, coordination, control,
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reconnaissance, equipping, training, and other tasks
carried out during the preparation process that are
essential for achieving the capabilities required to
accomplish assigned missions. During the search and
recovery operation in question, similar activities were
conducted, with emphasis placed primarily on
operation planning, force organization,
reconnaissance, and deployment of forces into the area
of operation, i.e., their operational development.
The planning of the aircraft search and recovery
operation was carried out by staff officers of the River
Flotilla Command and the 1st River Detachment. Their
primary task was to draft an operational order
encompassing all elements of the operation, i.e., to
define objectives, expected outcomes, methods for
achieving them, and the intent and decisions of
commanders. The planning process officially began
upon receipt of the operation execution order from
higher command on June 4, 2010, at 06:30 hour. Upon
receiving the mission, the unit commander organized
the decision-making process. The decision-making
process was conducted in accordance with the “Interim
Guidelines for Operational Planning and Command
Work in the Serbian Armed Forces", and followed the
prescribed seven-phase procedure [4]:
− Phase 1. Initiation
− Phase 2. Orientation
− Phase 3. Development of Courses of Action
− Phase 4. Analyses of Courses of Action (war games)
− Phase 5. Comparison of Courses of Action
− Phase 6. Approval of Courses of Action
− Phase 7. Development of Operational Documents
The greatest challenge faced by the command was
how to best respond to the crisis, specifically, how to
approach problem-solving using a modular principle,
as required by the nature of the task. The solution was
found in the combined use of diving and pontoon
units, which, although very different in purpose and
equipment, were highly complementary and effective
for this mission. The planning process was completed
by 09:30 hours on the same day and formed an integral
part of the comprehensive preparations, primarily led
by the Commander of the River Flotilla and his
command, i.e., the Operational Planning Group (OPG).
The Organization of forces required an integrated
approach involving various units of the Serbian Armed
Forces, structured into command forces, task execution
forces and logistical support forces. The command
forces were composed of staff officers from different
specialties. Due to the wide scope and the involvement
of various defence system forces and certain security
system institutions, the key role of the command forces
was coordinating and directing all participants within
the operational zone.
The task execution forces were designated to
implement the adopted decision and directly carry out
specific non-combat tasks. As previously mentioned,
the generated task execution forces consisted of diving
and pontoon units. However, the key role in the
execution of the operation was held by the diving unit,
which was responsible for locating the aircraft,
assessing damage, and recovering it from the lake. The
pontoon units played a supporting role, tasked with
providing necessary surface support by forming a
floating platform and assisting in lifting the aircraft
from the lakebed. Cooperation between the diving and
pontoon units enabled the successful integration of
underwater and surface activities. The equipment and
resources used during the operation included the
following: light diving gear, a diving compressor, a
portable recompression chamber, a Zodiac inflatable
boat, an underwater sonar model SSK 600, floating
elements from the PM-71 pontoon bridge, tugboats
type RPP M-68, military motor vehicles (PUH G300,
TAM-110, TAM-150, FAP 2026 BDS, FAP 2026 AVG,
Zastava Rival van) and a Coles Hydra Husky mobile
crane.
The logistical support forces were composed of
logistical units from the 98
th
Air Base, which was
located near the operational zone. These units were
responsible for providing the participants of the
operation with accommodation, food, and other
logistical needs.
Reconnaissance is a process conducted during the
planning phase of an operation in order to ensure the
quality of the decision-making. The main objective of
reconnaissance in this operation was to gather as much
information as possible about the crash site, access
routes, potential locations for assembling and storing
equipment, the prevailing conditions in the operation
zone, as well as the specific characteristics of that zone
in comparison to the usual operational environment of
the engaged units (inland waterways – rivers).
Deployment of forces into the operational zone, or
their operational development, is the process through
which forces are timely positioned in favourable
locations to carry out the assigned mission. This is
achieved by grouping forces in time and space, as well
as forming the operational layout according to the
commander's decision. The process is considered
complete once all forces occupy their initial positions
[2]. The main challenge in this case was to quickly and
safely transport all the search and recovery equipment
to a relatively inaccessible area that was atypical for the
engaged units, which usually operate in riverine
environments. However, through effective planning
and data gathering during the planning phase, this
challenge was successfully addressed.
The commander of the diving unit received the task
at 09:30 hours and immediately issued orders for the
unit to prepare for transport to the operational zone as
quickly as possible. At 12:00 hours, twelve members
from the diving company departed for Gruža Lake
using the following vehicles: a PUH G300 utility
vehicle, a Zastava Rival van, a TAM 110 truck
equipped with a portable recompression chamber and
a TAM 150 vehicle for diver accommodation. The final
position for task execution within the operation zone
was reached by 15:00 hours on June 4, 2010, (in less
than nine hours of operational time). The remaining
equipment and assets, primarily from the pontoon
unit, were deployed in the second wave, and by 17:30
hours on the same day, their operational development
was completed, thereby officially concluding the
preparation phase of the operation.
3.2 Execution Phase of the Operation
The development of a search plan based on an
innovative - newone search method, which for the
purposes of this paper will be referred to as the EAGLE
METHOD (Figure 3), provided an original solution and
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represented a crucial step in achieving the desired
objective, which consisted of the following steps: 1)
defining a wider search area (based on available
information), 2) the use modern equipment with
applying an appropriate search method, and 3) the use
of divers with applying a suitable underwater search
method. In essence, the EAGLE METHOD solved the
challenge of locating a sunken object into big water
surface, with insufficient reliable data about aqurrate
position, through a step-by-step approach. First, a
wider search area was defined based on available
information about the aircraft's crash. Then, this area
was narrowed down through the use of appropriate
technical means (sonar, in this case). Finally, once the
search area was reduced to a micro-location, the
location and precise identification of the sunken object
were carried out by divers, whose deployment was
clearly defined in the diving plan. Choosing the right
search method is a key element of the plan, as the
success of the operation often depends on that decision
which must be adapted to specific conditions of
searching.
Figure 3. Eagle method of searching
Upon arrival in the operational zone (15:00 hours on
June 4, 2010), a data collection effort was organized to
determine the approximate location where the aircraft
had sunk into the lake, with the goal of defining a
wider search area. Eyewitnesses’ interviews proved to
be of great significance at this stage. Although their
statements regarding the aircraft's crash location were
quite contradictory, through analysis and cross-
referencing of all collected data, some useful
information was obtained. As a result, the search area
was reduced from 900 hectares to 92 hectares (Figure
4). This information later proved to be crucial for
locating the aircraft and for preventing chemical
contamination of the reservoir.
Figure 4. Wide area of searching
After defining the wider search area, the searching
way is chosen depending on the size of the aquatic
area, and it is carried out either using technical
equipment or divers. Given the large surface area
involved and the assessment that the object had not
sunk deeply into the mud, it was decided to initially
use a technical equipment- specifically, an American-
made sonar system, the SSS JW Fishers 600 (Figure 5.)
[5].
Figure 5. SSS-100K/600K side-scan sonar system by JW
Fishers (USA)
After selecting the searching way and assessing the
conditions prevailing in the aquatic area (such as
current, depth, width, and weather conditions), a
decision is made on which search method to apply. For
this particular case, the parallel course method was
chosen which is mainly used for large areas and is
suitable for both types of searches (using technical
equipment or divers). This method is characterized by
the simplicity of constructing the search polygon and a
high level of reliability in locating sunken objects, due
to the overlapping of search lanes during the
application of this method (Figure 6) [6].
Figure 6. Search lanes.
At exactly 17:50 hours on June 4, 2010, the search of
the water area began using the SSS JW Fishers 600
sonar, applying the parallel course method. After 120
minutes (at 19:50 hours on June 4, 2010), an object
resembling an aircraft was detected (Figure 7). Its
position within the wider search area was then marked
with diver buoys.
Figure 7. The contours of the sunken aircraft captured by the
sonar.
15
For this type of search, the selected equipment has
proven to be highly effective, as the use of sonar
provided minimal search time for an extremely large
area (120 minutes for about 90) with minimal strain on
personnel. The main characteristics of the SSS JW
FISHERS 600 sonar are shown in Table 1.
Table 1. Technical specifications for the SSS JW FISHERS 600
sonar
Frequency
Beam width:Х*В
Pulse duration
Output power
Мaximum range
Maximum depth
Tow speed
Dimensions of sonar fish
Diameter
Length
Weight
Cable length
Since the use of sonar significantly reduced the
search area, the process of locating the sunken aircraft
continued the following day (June 5, 2010) by applying
a different searching way — this time using divers.
Unlike the previous day, this time the search method
entailed the concentric circle method (Figure 8).
The method is typically used in still waters though
it can be applied in mild currents. The principle of the
search is as follows: a diver anchors a rope and then
swims in a clockwise direction (or counterclockwise).
After completing a full circle, the diver increases the
distance from the center, and repeats it. If the target
object is not found, the center is shifted by a distance
equal to two radii of the largest search circle, reduced
by the overlap zone. This method is complementary to
the previous one, as it is used for searching micro-
locations, providing high reliability and a strong
probability of detecting the sunken object [6].
Figure 8. Search using the concentric circle method.
The divers activities are previously defined in a
particular document called the dive plan, which, based
on all prior analyses, collected data, and required
actions, defines the following elements:
− Diving conditions: very difficult (depth up to 15 m
and visibility from 15 to 20 cm)
− Diving equipment selection: light diving gear with
open-circuit breathing apparatus
− Breathing medium: medical-grade air
− Diving method: buddy diving
− Search method: concentric circles
− Communication: Prearranged signals
− Diving safety measures: immediate (presence of
medical personnel and a portable recompression
chamber)
Prior to searching the aquatic area by using divers,
between 07:00 and 09:00 hours on June 5, 2010, due to
poor visibility in the lake (at depth from 15 to 20 cm)
members of the diving company went to the airport in
order to familiarize themselves with the shape and
construction of the aircraft by inspecting the same type
of aircraft located on the parking stand. This activity
proved crucial to the success of the operation, as
acquired knowledge enabled the divers, despite low
visibility, to identify key points necessary for safely
rigging lifting slings under the aircraft for extraction.
The dive by a diver pair began at 10:00 hours. At
depths ranging from 7 to 12 meters, the divers held
hands and applied the concentric circle method,
swimming counterclockwise. After 45 minutes of
diving under extremely difficult conditions, the divers
felt something that resembled the aircraft. Upon
further inspection, it was determined to be the J-22
ORAO aircraft, intact, although its nose section was
crushed up to behind the cockpit. The divers then tied
a buoy to the aircraft and surfaced. On the surface, they
were handed lifting slings to pass under the aircraft
and discuss how to carry out the operation. They
returned to the tail section of the aircraft and rigged a
sling underneath it, and then proceeded to the nose
section. Despite extremely difficult conditions, after
almost an hour of diving (by 11:45 hours), they
succeeded in threading the slings and let the buoy
bring them to the surface where they were secured to
the crane hook.
Due to worsened visibility caused by the
underwater activity, it was decided to pause the
operation to allow silt to settle, ensuring optimal
conditions for the final inspection of the sunken object
before lifting it to the surface. Upon revisiting the
aircraft, it was confirmed that the slings were properly
placed and the aircraft was ready to be lifted. The
signal was given to the crane operator to begin lifting,
and after lifting it 3 meters above the lakebed, the
process was paused for an additional inspection. Once
it was confirmed that there were no serious obstacles
to proceeding, the signal was given for final extraction.
At exactly 13:40 hours, the tail of the aircraft
emerged on the lake’s surface (Figure 9). For safety
reasons, it was decided not to extract the aircraft at the
current pontoon location, but instead to tow it and
pontoon platform to the lake shore where the aircraft
would be extracted in shallow water. There, due to a
lower risk of an environmental incident, it would be
transferred onto the pontoon. The main reason was the
risk of the aircraft's structural failure due to its current
condition, which could potentially result in the fuel
leak into Gruža Lake and cause an environmental
disaster.
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Figure 9. The moment when the tail of the aircraft emerged
on the lake’s surface.
The towing of the aircraft to the shore of the lake
took about 45 minutes, after which the aircraft was
safely pulled from the shallow part of the lake with the
help of a Coles Hydra Husky auto crane, and then to
the shore of the lake, as shown in Figure 10.
Figure 10. The extracted aircraft on the pontoon scaffold.
The extraction of the aircraft to the shore of Gruža
Lake marked the completion of the second phase of the
military operation (execution phase), and the final
activities were initiated, including the disengagement
of forces in the stabilization phase.
3.3 Stabilization phase
Engagement of units, in accordance with the level of
stabilization of the situation in the operation zone,
gradually began to reduce military capacities. The first
to disengage were the diving units, which, after
securing their equipment and resources, departed for
the base "Aleksandar Berić" in Novi Sad at 16:30 hours
on June 5, 2010. The remaining units sequentially left
the operation zone in accordance with the provided
instructions and orders.
Upon arrival at the home locations (at 19:30 hours),
the equipment was unpacked, and an analysis of the
task execution was conducted with the aim of
generating lessons learned based on the acquired
experiences.
The gained knowledge and experiences during the
operation provide a solid foundation for the quality
preparation of future similar operations and serve as a
source of information for revising existing doctrinal
documents. The application of new measures,
activities, and procedures based on lessons learned
prevents the repetition of mistakes and oversights that
could occur during the execution of future tasks.
4 LESSONS LEARNED AND ACQUIRED
EXPERIENCES
The task was received at 06:30 hours on June 4, 2010,
and its implementation lasted a total of 33 hours and 30
minutes, with the aircraft being retrieved to the shore
at exactly 16:00 hours the following day. This was a
remarkable achievement, considering the task’s
complexity and an uncertain outcome. Of the total
time, only one-sixth (3 hours) was spent on planning
the operation to leave as much time as possible for the
actual execution of the assigned task. The fast and
efficient planning of the operation by the command
(commanding forces) resulted from excellent training
of the officers for planning and high-quality staff
assessments.
The preparation, organization, and deployment of
forces to perform tasks in the operation zone, followed
by the search, discovery, and extraction of the sunken
aircraft from Gruža Lake, were also carried out
efficiently (30 hours and 30 minutes). Several reasons
contributed to this, but the most significant factors
were as follows:
− The training of divers to carry out a wide range of
tasks
− The application of up-to-date technology (the SSS
JW FISHERS600 sonar)
− A modular approach in the formation of forces to
perform the task (joint work of diving and pontoon
units)
− Problem-solving for searching large water areas by
creating an original Search Plan (EAGLE
METHOD) consisting of three elements: 1) defining
a wider search area, 2) conducting the search using
up-to-date technology and narrowing down the
search area to a micro-location and 3) diving search
(detailed and precise) with applying an appropriate
search technique.
− An original approach to solving underwater work
problems in conditions of low visibility (the use of
an aircraft of the same type at the airport parking
stand as a real model for familiarizing divers with
structural solutions).
− The doctrinal solutions foresee twice as much time
for planning the operation – 1/3 Planning
Instructions.
− An original approach to solving the problem of
lifting sunken objects without the presence of a
floating crane (using a pontoon scaffold with an
auto crane instead of a floating crane).
− Logistical support provided by local units of the
Serbian Armed Forces.
However, despite the positive aspects, some
shortcomings were identified during the
implementation of the search and recovery operation
of the sunken aircraft, such as:
− Limited autonomy of the laptop used for sonar
image projection (battery life is 2 hours; it needs to
be recharged thereafter).
− Lack of certain specific equipment for underwater
work, such as pneumatic cutters, underwater
suction pumps, etc.
17
− Inability to use floating cranes with higher tonnage
for lifting the load.
Additionally, the analysis of the operation's Gantt
chart (Figure 11) shows that the operational time for
the preparation phase and execution phase was almost
identical, which indicates that the search and recovery
operation of the sunken aircraft was carried out very
efficiently and effectively. For these reasons, the
applied measures, activities, and conceptual solutions
during the execution of this task can serve as a
paradigm for future similar non-combat operations.
Figure 11. Gannt chart of the operations
5 CONCLUSIONS
The case study presented innovative solutions for the
execution of very complex and dynamic tasks. The
modular approach to problem-solving, where the use
of diving and pontoon units ensured successful
interaction and complementarity between underwater
work and surface activities, represents a key element in
the success of such and similar non-combat operations.
Additionally, the effective application of
appropriate search methods, but through a completely
different approach, definitely increases the likelihood
of locating a sunken object in a large body of water with
very few reliable details about the exact location. By
developing an original search plan, the optimal
number of personnel and resources can be engaged
within an acceptable time frame. This approach is
highly valuable in crisis situations that require a quick
and efficient response.
Finally, the greatest contribution of this work is the
fact that all the data, experiences, and knowledge
related to the search and recovery operation of the
sunken aircraft are consolidated in one place. This can
generate a paradigm of best practices, useful for the
successful execution of future similar search and rescue
tasks.
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[2] “The Serbian armed forces operational doctrine”, Belgrad,
General Staff of the Serbian Armed forces, 2012.
[3] Š. Bajrami, “Model of use of river flotile in operation to
assist civil authorities in the event of floods”, Ph. D.
dissertation, University of Defence – Military academy,
Belgrade, R. Serbia, 2022.
[4] “Manual for operational planning and work of commands
in the Serbian Armed forces”, Belgrad, General Staff of
the Serbian Armed forces, 2017.
[5] Technical characteristics of the sonar "SSS JW FISHERS
600", https://www.jwfishers.com/product/side-scan-
sonar-600-khz, accessed May 20, 2015.
[6] V. Vukovic, “Three-star diver training material P-3”,
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