RUSTOM II is a Medium-Altitude Long-Endurance (MALE) Unmanned Aerial Vehicle (UAV) with an endurance of 24 hours and the ability to fly up to 25000 feet altitude.  It has multiple payload capabilities to support both daytime and nighttime operations. The retractable landing gear system consists of dual redundant microcontrollers. The Landing Gear Controller (LGC) is required to execute and monitor the retraction, deployment, and brake sequence of the landing gear based on the command received from the Flight Control Computer (RFCC). The LGC is connected to the RFCC through the MIL1553B interface.  The RFCC acts as a bus controller (BC), and the LGC acts as a remote terminal (RT), with software-programmable RT addresses 22 (active) and 23 (standby).  However, provision is made to set the RT addresses through hardware. LGC has dual redundant 32-bit microcontrollers in the main/hot standby configuration. When the main controller fails, the hot standby controller executes the operations.  The main controller and standby controller are interfaced via a cross-channel data link (CCDL) asynchronous RS422 interface. LGC is connected to the RFCC via the 1553B bus for receiving commands,  to the nose and main landing gears through analog input via ADC and duplex discrete I/O, and to the hydraulic motor pump via analog input and discrete output.  The LGC software performs the following functionalities:. Perform modes of operation like retraction, deployment, brake, emergency deployment, and emergency brake based on the RFCC command. Activate the landing gear subsystem assemblies like the hydraulic power pack, retraction, deployment, brake, bypass, and emergency valves. Monitor the subsystem assembly, like wheel speed, weight on the wheel, hydraulic pressure, valve pressure, and actuator end-limit switches, and post the status to the RFCC. Perform Power on Self Test (POST), Initiated Pre-flight Built-In Test (PBIT), and Continuous Built-In Test (CBIT) functionalities. Output the parameters to telemetry.

1. AVIONICS CASE STUDY –
IV&V OF LANDING GEAR CONTROLLER (LGC)
FOR AN UNMANNED AERIAL VEHICLE
Oak Systems Pvt. Ltd.

2. About LGC
The Landing gear controller was meant for a Military Unmanned
Aerial Vehicle.
The landing gear system consists of redundant controller
in master/slave hot standby configurations to meet the fault
tolerant requirement. Each controller consists of single identical
computer software configuration item (CSCI) capable of
performing the software functionalists The LGC software
shall be able to read inputs from MIL1553B, Analog &
discrete interfaces like limit switches, Pressure sensors, wheel
speed sensors, Current sensor and process inputs, perform
data validity, persistency checks, perform PBIT, CBIT, execute
the RFCC command, send outputs through Analog, Discrete and
MIL1553B interfaces.
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
2

3. Salient features of the System
v Redundancy management
v Retraction
v Deployment
v Emergency Deployment
v Braking
v Emergency braking
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
3

4. Major System Functionality Explained -
Deployment
Deployment involves a complex sequential steps with
several checks in the process
v Weight on wheel status, hydraulic mode
v Hydaulic pressure
v Status of limit switches
v Emergency deployment involving the same steps but with
pneumatic pressure
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
4

5. Major System Functionality Explained -
Braking
Braking involves a complex sequential steps with several
checks in the process
v Successful Deployment
v Hydaulic pressure
v Wheel speed
v Emergency Braking involving the same steps but with
pneumatic pressure
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
5

6. Trigger for IV&V
As per DO-178B guidelines Independent Verification &
Validation (IV&V) was mandated for DAL (Design
assurance level A with object code verification)
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
6

7. Scope of Work
To Conduct IV&V as per RTCA - DO178B Level ‘A’ compliance -
v Planning phase docs review e.g. PSAC, SVP, SDP, SCMP, SQAP, SRS, SDS, SCS
v High level Requirement Verification
v Low level Requirement (Design) Verification
v Code Evaluation (MISRA Standards)
v Requirement based test case preparation (High level and Low level Tests) for 100%
Requirement coverage
v Source Code coverage (100% MC/DC) and Object code verification
v High Level and Low level Test Execution (using LDRA tool)
v Traceability analysis:
§ Requirements ó Design ó Code
§ Requirement ó High level Tests
§ Design ó Low level Tests
v Software Configuration Audit
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
7

8. In the Works
v 9000 Lines of C code
v Duration was 6 months
v Requirement capture tool IBM DOORS and Design Tool IBM Rhapsody
was used
v Verification Tool used was LDRA, TBREQ of LDRA for traceability,
ObjectBox for Object code verification
v Team size ranging from 4 - 8
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
8
Software Size: 9 KLOC
Language: C

9. Accomplishments
v Provided templates and checklists meeting DO178B guidelines
v Thorough plan document review with emphasis on safety measures needed as a suggestion
v Requirement and design review : Uncovered anomalies in the document in form of
traceability, completeness and correctness w.r.t to DO-178B standards
v Test case creation at both HSI and Unit level with emphasis on uncovering faults to make
system robust by adopting testing techniques like BVA, Equivalence partitioning, arithmetic
precision, fault recovery.
v Extensive validation involving complex conditions in execution of all syetem functionalities end
- to -end
v Test case execution at both levels with emphasis on 100 percent requirement coverage, 100
percent MC/DC coverage, 100 percent branch coverage, 100 percent statement coverage
v Object code verification using LDRA objectbox
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
9

10. Outcome
Activity/Task Status
Review report of Plan Docs:
PSAC, SDP, SCMP, SRS, SDS, SCS, SQAP, SVP
Delivered
SRD Review report
Delivered
HLR SVCP Preparation
Delivered
SDD Review report
Delivered
LLR SVCP Preparation
Delivered
Code Review report
Delivered
SDD-Code Traceability
Delivered
LLR Test Execution, Object code verification
Delivered
HLR Test Execution
Delivered
IVV Reports (SCI, SECI, SAS)
Delivered
Copyright © 2020 Oak Systems Private Limited. All Rights Reserved
10

11. Thank you!
Oak Systems Pvt. Ltd.
#27, NGEF Lane, Off 100 Feet Road,
Indira Nagar, Bengaluru – 560 038, INDIA
Tel : +91-80-4126 7681
Email: contact@oaksys.net
URL: www.oaksys.net
We add value through engagement