Here’s what we know so far by visually observing the crash of the Ecuadorian Air Force-owned Dhruv ALH at Quito on October 27: of the three Dhruv ALHs flying over an air base during celebrations to mark the 89th anniversary of the air force, one of them apparently swung 90 degrees and started losing altitude. As the video clip of the incident shows, the two-man aircrew who are in all probability highly experienced aviators, instinctively resorted to the autorotation technique (the only available option) to regain control and to their credit it must be said that they did succeed in slowing the rate of descent, although within the available 8 seconds, they could not stabilise the helicopter, which in turn led to a half-controlled descent and touchdown, with the stricken Dhruv ALH coming to rest on its portside, with the two-man aircrew managing to leave the helicopter by themselves after the crash before being taken to Quito's Military Hospital. The video clipping also showed the Dhruv ALH’s main rotor blades and tail rotor blades functioning, but not enough to indicate if the tail-rotor hub and tail-rotor shaft were in a fully functional state. Based purely on the available video clipping, it would seem that:
• The ill-fated Dhruv PROBABLY suffered from a sudden loss of power in either one of its twin Ardiden-1H (Shakti) engines, jointly built by HAL and Turbomeca. But catastrophic failure of both engines or failure of both the LH and RH sides of the main gearbox (MGB) can be ruled out. It is also PROBABLE that either one of the two fuel supply tanks (which supply fuel independently to the two engines) was starved of fuel-flow from the the Dhruv ALH’s three main fuel tanks, which house the pumps required for ensuring the fuel-flow to the fuel supply tanks.
• The above two probabilities PROBABLY contributed to the sudden reduction of supply of power to the tail-rotor gearbox via the tail-rotor drive shaft, resulting in the helicopter veering off to the left while losing altitude at the same time.
The only saving grace then, and the only available option for the aircrew then was to resort to the autorotation technique, which they did and that is probably the only reason they were fortunate enough to survive to fly again in future. Full marks to them!—Prasun K. Sengupta
I am enclosing below all the FAR Part 29standards that the Dhruv ALH complies with. FAR Part 29: Airworthiness Standards: Transport Category Rotorcraft
Federal Aviation Regulations Subpart A - General
o Sec. 29.1 - Applicability.
o Sec. 29.2 - Special retroactive requirements.Subpart B - Flight
o Sec. 29.21 - Proof of compliance.
o Sec. 29.25 - Weight limits.
o Sec. 29.27 - Center of gravity limits.
o Sec. 29.29 - Empty weight and corresponding center of gravity.
o Sec. 29.31 - Removable ballast.
o Sec. 29.33 - Main rotor speed and pitch limits.
o Sec. 29.45 - General.
o Sec. 29.49 - Performance at minimum operating speed.
o Sec. 29.51 - Takeoff data: general.
o Sec. 29.53 - Takeoff: Category A.
o Sec. 29.55 - Takeoff decision point (TDP): Category A.
o Sec. 29.59 - Takeoff path: Category A.
o Sec. 29.60 - Elevated heliport takeoff path: Category A.
o Sec. 29.61 - Takeoff distance: Category A.
o Sec. 29.62 - Rejected takeoff: Category A.
o Sec. 29.63 - Takeoff: Category B.
o Sec. 29.64 - Climb: General.
o Sec. 29.65 - Climb: All engines operating.
o Sec. 29.67 - Climb: One engine inoperative (OEI).
o Sec. 29.71 - Helicopter angle of glide: Category B.
o Sec. 29.75 - Landing: General.
o Sec. 29.77 - Landing Decision Point (LDP): Category A.
o Sec. 29.79 - Landing: Category A.
o Sec. 29.81 - Landing distance: Category A.
o Sec. 29.83 - Landing: Category B.
o Sec. 29.85 - Balked landing: Category A.
o Sec. 29.87 - Height-velocity envelope.
o Sec. 29.141 - General.
o Sec. 29.143 - Controllability and maneuverability.
o Sec. 29.151 - Flight controls.
o Sec. 29.161 - Trim control.
o Sec. 29.171 - Stability: general.
o Sec. 29.173 - Static longitudinal stability.
o Sec. 29.175 - Demonstration of static longitudinal stability.
o Sec. 29.177 - Static directional stability.
o Sec. 29.181 - Dynamic stability: Category A rotorcraft.
o Sec. 29.231 - General. o Sec. 29.235 - Taxiing condition.
o Sec. 29.239 - Spray characteristics.
o Sec. 29.241 - Ground resonance.
o Sec. 29.251 - Vibration.Subpart C - Strength Requirements
o Sec. 29.301 - Loads.
o Sec. 29.303 - Factor of safety.
o Sec. 29.305 - Strength and deformation.
o Sec. 29.307 - Proof of structure.
o Sec. 29.309 - Design limitations.
o Sec. 29.321 - General.
o Sec. 29.337 - Limit maneuvering load factor.
o Sec. 29.339 - Resultant limit maneuvering loads.
o Sec. 29.341 - Gust loads.
o Sec. 29.351 - Yawing conditions.
o Sec. 29.361 - Engine torque.
o Sec. 29.391 - General.
o Sec. 29.395 - Control system.
o Sec. 29.397 - Limit pilot forces and torques.
o Sec. 29.399 - Dual control system.
o Sec. 29.411 - Ground clearance: tail rotor guard.
o Sec. 29.427 - Unsymmetrical loads.
o Sec. 29.471 - General.
o Sec. 29.473 - Ground loading conditions and assumptions.
o Sec. 29.475 - Tires and shock absorbers.
o Sec. 29.477 - Landing gear arrangement.
o Sec. 29.479 - Level landing conditions.
o Sec. 29.481 - Tail-down landing conditions.
o Sec. 29.483 - One-wheel landing conditions.
o Sec. 29.485 - Lateral drift landing conditions.
o Sec. 29.493 - Braked roll conditions.
o Sec. 29.497 - Ground loading conditions: landing gear with tail wheels.
o Sec. 29.501 - Ground loading conditions: landing gear with skids.
o Sec. 29.505 - Ski landing conditions.
o Sec. 29.511 - Ground load: unsymmetrical loads on multiple-wheel units.
o Sec. 29.519 - Hull type rotorcraft: Water-based and amphibian.
o Sec. 29.521 - Float landing conditions.
o Sec. 29.547 - Main and tail rotor structure.
o Sec. 29.549 - Fuselage and rotor pylon structures.
o Sec. 29.551 - Auxiliary lifting surfaces.
o Sec. 29.561 - General.
o Sec. 29.562 - Emergency landing dynamic conditions.
o Sec. 29.563 - Structural ditching provisions.
o Sec. 29.571 - Fatigue evaluation of structure.Subpart D - Design and Construction
o Sec. 29.601 - Design.
o Sec. 29.602 - Critical parts.
o Sec. 29.603 - Materials.
o Sec. 29.605 - Fabrication methods.
o Sec. 29.607 - Fasteners.
o Sec. 29.609 - Protection of structure.
o Sec. 29.610 - Lightning and static electricity protection.
o Sec. 29.611 - Inspection provisions.
o Sec. 29.613 - Material strength properties and design values.
o Sec. 29.619 - Special factors.
o Sec. 29.621 - Casting factors.
o Sec. 29.623 - Bearing factors.
o Sec. 29.625 - Fitting factors.
o Sec. 29.629 - Flutter and divergence.
o Sec. 29.631 - Bird strike.
o Sec. 29.653 - Pressure venting and drainage of rotor blades.
o Sec. 29.659 - Mass balance.
o Sec. 29.661 - Rotor blade clearance.
o Sec. 29.663 - Ground resonance prevention means.
o Sec. 29.671 - General.
o Sec. 29.672 - Stability augmentation, automatic, and power-operated systems.
o Sec. 29.673 - Primary flight controls.
o Sec. 29.674 - Interconnected controls.
o Sec. 29.675 - Stops.
o Sec. 29.679 - Control system locks.
o Sec. 29.681 - Limit load static tests.
o Sec. 29.683 - Operation tests.
o Sec. 29.685 - Control system details.
o Sec. 29.687 - Spring devices.
o Sec. 29.691 - Autorotation control mechanism.
o Sec. 29.695 - Power boost and power-operated control system.
o Sec. 29.723 - Shock absorption tests.
o Sec. 29.725 - Limit drop test.
o Sec. 29.727 - Reserve energy absorption drop test.
o Sec. 29.729 - Retracting mechanism.
o Sec. 29.731 - Wheels.
o Sec. 29.733 - Tires.
o Sec. 29.735 - Brakes.
o Sec. 29.737 - Skis.
o Sec. 29.751 - Main float buoyancy.
o Sec. 29.753 - Main float design.
o Sec. 29.755 - Hull buoyancy.
o Sec. 29.757 - Hull and auxiliary float strength.
o Sec. 29.771 - Pilot compartment.
o Sec. 29.773 - Pilot compartment view.
o Sec. 29.775 - Windshields and windows.
o Sec. 29.777 - Cockpit controls.
o Sec. 29.779 - Motion and effect of cockpit controls.
o Sec. 29.783 - Doors.
o Sec. 29.785 - Seats, berths, litters, safety belts, and harnesses.
o Sec. 29.787 - Cargo and baggage compartments.
o Sec. 29.801 - Ditching.
o Sec. 29.803 - Emergency evacuation.
o Sec. 29.805 - Flight crew emergency exits.
o Sec. 29.807 - Passenger emergency exits.
o Sec. 29.809 - Emergency exit arrangement.
o Sec. 29.811 - Emergency exit marking.
o Sec. 29.812 - Emergency lighting.
o Sec. 29.813 - Emergency exit access.
o Sec. 29.815 - Main aisle width.
o Sec. 29.831 - Ventilation.
o Sec. 29.833 - Heaters.
o Sec. 29.851 - Fire extinguishers.
o Sec. 29.853 - Compartment interiors.
o Sec. 29.855 - Cargo and baggage compartments.
o Sec. 29.859 - Combustion heater fire protection.
o Sec. 29.861 - Fire protection of structure, controls, and other parts.
o Sec. 29.863 - Flammable fluid fire protection.
o Sec. 29.865 - External loads.
o Sec. 29.871 - Leveling marks.
o Sec. 29.873 - Ballast provisions.Subpart E - Powerplant
o Sec. 29.901 - Installation.
o Sec. 29.903 - Engines.
o Sec. 29.907 - Engine vibration.
o Sec. 29.908 - Cooling fans.
o Sec. 29.917 - Design.
o Sec. 29.921 - Rotor brake.
o Sec. 29.923 - Rotor drive system and control mechanism tests.
o Sec. 29.927 - Additional tests.
o Sec. 29.931 - Shafting critical speed.
o Sec. 29.935 - Shafting joints.
o Sec. 29.939 - Turbine engine operating characteristics.
o Sec. 29.951 - General.
o Sec. 29.952 - Fuel system crash resistance.
o Sec. 29.953 - Fuel system independence.
o Sec. 29.954 - Fuel system lightning protection.
o Sec. 29.955 - Fuel flow.
o Sec. 29.957 - Flow between interconnected tanks.
o Sec. 29.959 - Unusable fuel supply.
o Sec. 29.961 - Fuel system hot weather operation.
o Sec. 29.963 - Fuel tanks: general.
o Sec. 29.965 - Fuel tank tests.
o Sec. 29.967 - Fuel tank installation.
o Sec. 29.969 - Fuel tank expansion space.
o Sec. 29.971 - Fuel tank sump.
o Sec. 29.973 - Fuel tank filler connection.
o Sec. 29.975 - Fuel tank vents and carburetor vapor vents.
o Sec. 29.977 - Fuel tank outlet.
o Sec. 29.979 - Pressure refueling and fueling provisions below fuel level.
o Sec. 29.991 - Fuel pumps.
o Sec. 29.993 - Fuel system lines and fittings.
o Sec. 29.995 - Fuel valves.
o Sec. 29.997 - Fuel strainer or filter.
o Sec. 29.999 - Fuel system drains.
o Sec. 29.1001 - Fuel jettisoning.
o Sec. 29.1011 - Engines: general.
o Sec. 29.1013 - Oil tanks.
o Sec. 29.1015 - Oil tank tests.
o Sec. 29.1017 - Oil lines and fittings.
o Sec. 29.1019 - Oil strainer or filter.
o Sec. 29.1021 - Oil system drains.
o Sec. 29.1023 - Oil radiators.
o Sec. 29.1025 - Oil valves.
o Sec. 29.1027 - Transmission and gearboxes: general.
o Sec. 29.1041 - General.
o Sec. 29.1043 - Cooling tests.
o Sec. 29.1045 - Climb cooling test procedures.
o Sec. 29.1047 - Takeoff cooling test procedures.
o Sec. 29.1049 - Hovering cooling test procedures.
o Sec. 29.1091 - Air induction.
o Sec. 29.1093 - Induction system icing protection.
o Sec. 29.1101 - Carburetor air preheater design.
o Sec. 29.1103 - Induction systems ducts and air duct systems.
o Sec. 29.1105 - Induction system screens.
o Sec. 29.1107 - Inter-coolers and after-coolers.
o Sec. 29.1109 - Carburetor air cooling.
o Sec. 29.1121 - General.
o Sec. 29.1123 - Exhaust piping.
o Sec. 29.1125 - Exhaust heat exchangers.
o Sec. 29.1141 - Powerplant controls: general.
o Sec. 29.1142 - Auxiliary power unit controls.
o Sec. 29.1143 - Engine controls.
o Sec. 29.1145 - Ignition switches.
o Sec. 29.1147 - Mixture controls.
o Sec. 29.1151 - Rotor brake controls.
o Sec. 29.1157 - Carburetor air temperature controls.
o Sec. 29.1159 - Supercharger controls.
o Sec. 29.1163 - Powerplant accessories.
o Sec. 29.1165 - Engine ignition systems.
o Sec. 29.1181 - Designated fire zones: regions included.
o Sec. 29.1183 - Lines, fittings, and components.
o Sec. 29.1185 - Flammable fluids.
o Sec. 29.1187 - Drainage and ventilation of fire zones.
o Sec. 29.1189 - Shutoff means.
o Sec. 29.1191 - Firewalls.
o Sec. 29.1193 - Cowling and engine compartment covering.
o Sec. 29.1194 - Other surfaces.
o Sec. 29.1195 - Fire extinguishing systems.
o Sec. 29.1197 - Fire extinguishing agents.
o Sec. 29.1199 - Extinguishing agent containers.
o Sec. 29.1201 - Fire extinguishing system materials.
o Sec. 29.1203 - Fire detector systems.Subpart F - Equipment
o Sec. 29.1301 - Function and installation.
o Sec. 29.1303 - Flight and navigation instruments.
o Sec. 29.1305 - Powerplant instruments.
o Sec. 29.1307 - Miscellaneous equipment.
o Sec. 29.1309 - Equipment, systems, and installations.
o Sec. 29.1321 - Arrangement and visibility.
o Sec. 29.1322 - Warning, caution, and advisory lights.
o Sec. 29.1323 - Airspeed indicating system.
o Sec. 29.1325 - Static pressure and pressure altimeter systems.
o Sec. 29.1327 - Magnetic direction indicator.
o Sec. 29.1329 - Automatic pilot system.
o Sec. 29.1331 - Instruments using a power supply.
o Sec. 29.1333 - Instrument systems.
o Sec. 29.1335 - Flight director systems.
o Sec. 29.1337 - Powerplant instruments.
o Sec. 29.1351 - General.
o Sec. 29.1353 - Electrical equipment and installations.
o Sec. 29.1355 - Distribution system.
o Sec. 29.1357 - Circuit protective devices.
o Sec. 29.1359 - Electrical system fire and smoke protection.
o Sec. 29.1363 - Electrical system tests.
o Sec. 29.1381 - Instrument lights.
o Sec. 29.1383 - Landing lights.
o Sec. 29.1385 - Position light system installation.
o Sec. 29.1387 - Position light system dihedral angles.
o Sec. 29.1389 - Position light distribution and intensities.
o Sec. 29.1391 - Minimum intensities in the horizontal plane of forward and rear position lights.
o Sec. 29.1393 - Minimum intensities in any vertical plane of forward and rear position lights.
o Sec. 29.1395 - Maximum intensities in overlapping beams of forward and rear position lights.
o Sec. 29.1397 - Color specifications.
o Sec. 29.1399 - Riding light.
o Sec. 29.1401 - Anticollision light system.
o Sec. 29.1411 - General.
o Sec. 29.1413 - Safety belts: passenger warning device.
o Sec. 29.1415 - Ditching equipment.
o Sec. 29.1419 - Ice protection.
o Sec. 29.1431 - Electronic equipment.
o Sec. 29.1433 - Vacuum systems.
o Sec. 29.1435 - Hydraulic systems.
o Sec. 29.1439 - Protective breathing equipment.
o Sec. 29.1457 - Cockpit voice recorders.
o Sec. 29.1459 - Flight recorders.
o Sec. 29.1461 - Equipment containing high energy rotors.Subpart G-Operating Limitations and Information
o Sec. 29.1501 - General.
o Sec. 29.1503 - Airspeed limitations: general.
o Sec. 29.1505 - Never-exceed speed.
o Sec. 29.1509 - Rotor speed.
o Sec. 29.1517 - Limiting height-speed envelope.
o Sec. 29.1519 - Weight and center of gravity.
o Sec. 29.1521 - Powerplant limitations.
o Sec. 29.1522 - Auxiliary power unit limitations.
o Sec. 29.1523 - Minimum flight crew.
o Sec. 29.1525 - Kinds of operations.
o Sec. 29.1527 - Maximum operating altitude.
o Sec. 29.1529 - Instructions for Continued Airworthiness.
o Sec. 29.1541 - General.
o Sec. 29.1543 - Instrument markings: general.
o Sec. 29.1545 - Airspeed indicator.
o Sec. 29.1547 - Magnetic direction indicator.
o Sec. 29.1549 - Powerplant instruments.
o Sec. 29.1551 - Oil quantity indicator.
o Sec. 29.1553 - Fuel quantity indicator. o Sec. 29.1555 - Control markings.
o Sec. 29.1557 - Miscellaneous markings and placards.
o Sec. 29.1559 - Limitations placard.
o Sec. 29.1561 - Safety equipment.
o Sec. 29.1565 - Tail rotor.
o Sec. 29.1581 - General.
o Sec. 29.1583 - Operating limitations.
o Sec. 29.1585 - Operating procedures. o Sec. 29.1587 - Performance information.
o Sec. 29.1589 - Loading information.Appendices• Appendix A to Part 29 - Instructions for Continued Airworthiness • Appendix B to Part 29 - Airworthiness Criteria for Helicopter Instrument Flight • Appendix C to Part 29 - Icing Certification • Appendix D to Part 29 - Criteria for Demonstration of Emergency Evacuation Procedures Under §29.803
The military variants of the Dhruv ALH adhere to the following FAR/MILSPEC standards:
The military variants of the Dhruv ALH adhere to the following FAR/MILSPEC standards:
US Army Aeronautical Design Standard-33E (ADS-33E)Flaw-Tolerant Rotor System: FAR/JAR 29.571,
AM 29-28Crashworthy Fuel System: FAR/JAR 29.952,
AM 29-35Flaw-Tolerant Drive Train with Over Torque Certification: FAR/JAR 29.952, AM 29-28
Turbine Burst Protection: FAR/JAR 29.901, AM 29-36
Composite Spar Main & Tail Rotor Blades with Lightning Strike Protection: FAR/JAR 1309(h), AM 29-40
Engine Compartment Fire Protection: FAR/JAR 29.1193
Redundant Hydraulics & Flaw Tolerant Flight Controls: FAR/JAR 29.571, AM 29-28
Aircraft-Wide Bird Strike Protection: FAR/JAR 29.631, AM 29-40
Crashworthiness Standard: FAR/JAR 29.561, AM 29-38
Crashworthy Seats Conforming to MIL-STD-1472B
Cockpit Instrumentation Lighting Conforming to MIL-STD-85762A
Avionics Databus: MIL-STD-1553B or ARINC-429
Autopilot Accuracy: MIL-F-9490D
Embedded MIL-STD-188-141B ALE Link Protection
Embedded MIL-STD-188-110B data modem