Two IAF helicopters crash midair in Gujarat, 9 killed

Ray

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A very freak accident where the rotors could touch!

It is sad to lose so many in one crash, but what is most worrying is how and why were the helicopters practically flying at a handshake distance and that too laterally!
 

Ray

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CONSIDERATIONS
6-15. In terrain flight, a greater number of aircraft can be more easily detected than a lesser number. In addition, a larger group requires more terrain relief to remain concealed. If a large group is necessary for the mission, dispersion can be achieved by using numerous routes with small flights instead of one large flight. The enemy situation, however, may mandate the use of one route and mass concentration of troops, which would require the larger flight. In a well-planned tactical formation flight, at terrain-flight altitudes, individual aircraft within the flight move like individual infantrymen in a squad. Flight lead selects the general direction of travel, but within those boundaries, each aircraft picks the exact piece of terrain to fly over. The aviator of each aircraft must be careful not to maintain equal distances from preceding aircraft or fly over exactly the same terrain as preceding aircraft, as this will aid enemy ADA or small-arms fire.
TECHNIQUES OF MOVEMENT
6-16. Multi-aircraft operations in a high-threat environment may require greater flexibility than is possible with basic flight formations. The flexibility required to conduct multi-aircraft operations at lower terrain-flight altitudes is best achieved by employing maneuvering formations in conjunction with techniques of movement. The three methods of movement used when conducting multi-aircraft operations are traveling, traveling overwatch, and bounding overwatch.
Traveling
6-17. Traveling is used to move rapidly over the battlefield when enemy contact is unlikely, or the situation requires speed for evading the enemy. All aircraft move at the same speed. This technique is the fastest method for aircraft formation movement but provides the least amount of security. Units often employ low-level and contour flight at high airspeeds using the traveling movement technique.
Traveling Overwatch
6-18. Traveling overwatch is used when speed is essential and enemy contact is possible. This technique is normally associated with reconnaissance, security, and attack missions when threat and/or environmental conditions preclude use of bounding overwatch. Lead aircraft or teams move constantly, and trail aircraft or teams move as necessary maintaining overwatch of lead. Overwatching aircraft key their movement to terrain and distance from the main element. It also remains ready to fire or maneuver, or both, providing support to main elements. Units often employ contour or NOE flight with the traveling overwatch technique using high and varying airspeeds depending on weather, ambient light, and threat.
Bounding Overwatch
6-19. Bounding overwatch is used when enemy contact is expected and the greatest degree of concealment is required. It is the slowest movement technique; too slow for high-tempo operations and too vulnerable for non-linear and/or urban operations. Individual aircraft or aircraft teams employ alternate or successive bounds.
6-20. One element remains in position to observe, fire, or maneuver before the other element moves. Overwatching elements cover the progress of bounding elements from a covered and concealed position, which offers observation and fields of fire against potential enemy positions.
6-21. The length of the bound depends on terrain, visibility, and effective range of the overwatching weapon system. Units normally employ contour and NOE flight with the bounding overwatch technique. Airspeed during each bound is varied depending on availability of vegetation and terrain for concealment.
SIGHT PICTURE
6-22. Sight picture is a particular angle, based on particular components a trailing aircraft sees or cues on when flying in formation on another aircraft. This is based on aircraft type and may cue on formation lights–especially at night or with NVDs. An aviator must become proficient and comfortable with this sight picture as it allows an aviator to judge attitude changes and relative position to the preceding aircraft.
FORMATION ANGLE
6-23. This is the angle relative to the aircraft being followed in formation flight. Zero degrees would be directly behind and ninety degrees would be abeam. While the angle is traditionally 30 or 45 degrees (figure 6-1 ), it may have to be different due to aircraft limitations. For example, at a 45-degree viewing angle between aircraft, the UH-60 helicopter has windshield posts that obstruct the aviator's ability to see, mandating a slightly different angle to accommodate this design flaw.
FORMATION SEPARATION
6-24. The space between aircraft in any given formation represents a tradeoff between the previously mentioned formation characteristics. The capability of all members of the flight to navigate and avoid obstacles without the excessive concern of colliding with other flight members is a primary factor in determining formation spacing. METT-TC considerations drive spacing between aircraft. For example, low illumination nights usually require close spacing, while day flights can assume large separations, enhancing lead's ability to maneuver. In choosing a sound tactical formation, lead should consider the following factors and how they affect the formation:
l Threat.
l Terrain.
l Illumination,
l Time of day.
l Visibility.
l Communications environment.
l Capabilities of the crews and aircraft in the flight.
The wingman is ultimately responsible for maintaining adequate separation to prevent collision by anticipating (and providing clearance for) maneuvering by lead.
HORIZONTAL DISTANCE
6-25. Formations are defined and expressed in rotor diameters (based on type of aircraft being flown) between tip-path planes or the rearward edge of the disk on the leading aircraft and the forward edge of the disk on the trailing aircraft. This distance is usually predetermined during the mission brief and established by the chalk 2 aircraft in the flight. Aircraft after chalk 2 should follow the established pattern. Horizontal distance is defined as (figure 6-1 )—
l Tight. The horizontal distance for tight is approximately two rotor disks.
l Close. The horizontal distance for close is three to five rotor disks.
l Loose. The horizontal distance for loose is six to ten rotor disks.
l Extended. The horizontal distance for extended distance is more than ten rotor disks, as dictated by tactical requirements.



Vertical Separation
6-26. Flat, stepped-up (figure 6-2 ), and stepped down are vertical separations.
l Flat. All aircraft are flown at the same altitude.
l Stepped-up. Vertical separation of 1 to 10 feet higher between lead, chalk 2, and each successive aircraft.
l Stepped-down. Vertical separation of 1 to 10 feet lower between lead, chalk 2, and each successive aircraft.



Note. In stepped-down formation, trailing aircraft may experience wake turbulence. To avoid this turbulence, they will need to adjust their relative position. Trailing aircraft require more power to fly in this formation.

Flat Terrain
6-27. Generally, in flat terrain, formation separation should increase as such formations are more difficult to detect. If the enemy detects the formation, it must choose one helicopter and potentially lose SA on the second. This aircraft may pass completely unnoticed and provide mutual support. This is true for both air and surface threats.
Rough Terrain
6-28. Rough terrain may require closer formation spacing. The tactical advantages of wide formations must be balanced with the difficulty of controlling those formations in rough terrain. The formation selected should enhance cover and concealment of all aircraft in the flight and the ability for each member of the flight to select terrain and seek concealment while still maintaining SA on lead (visual contact is desired but not required at all times).

FORMATION TAKEOFF
6-31. A formation takeoff is two or more aircraft leaving the ground simultaneously and then maintaining a predesignated relative position during the takeoff. Most formation takeoffs are made from the ground and liftoff simultaneously at a prearranged signal from the lead aircraft. The leading aircraft should accelerate slightly faster than a VMC takeoff, allowing the following aircraft to gain translational lift; care must be taken, however, to not accelerate too quickly and leave the flight scrambling to catch up. The initial rate of climb must be enough to clear barriers with a safety margin. Trailing aircraft maneuver into the en route formation and attain a stepped-up vertical separation as soon as possible permitting acceleration and climb to undisturbed air. Once the flight is airborne and established, the lead aircraft can slowly and smoothly accelerate to normal climb or cruise airspeed. Takeoffs should only be into the wind, especially for dust/sand/snow conditions. For moderate to heavy dust/sand/snow conditions, aircraft should take-off separately in chalk order and then conduct an in-flight join-up.
FORMATION FLIGHT—EN ROUTE
6-32. Formation flying is the maneuvering of aircraft according to established TTP. It includes rapid, but controlled, change from a specific formation suitable for one set of conditions to another formation meeting requirements of an entirely different set of conditions. Safe and orderly formation flight is the result of extensive training, continuous practice, and a high degree of discipline.
6-33. The aviator flying each aircraft maneuvers with primary reference to only one other aircraft. The constant vigilance necessary to fly, reference the other aircraft, avoid obstacles, and incorporate an instrument scan precludes the P* from observing other aircraft. However, P can observe aircraft other than the primary reference aircraft. In formation types requiring observation of two aircraft such as diamond or staggered, the P* must do so with great care and precision while mainly viewing the primary aircraft.
6-34. Aviators must anticipate aerodynamic interference between aircraft during formation flight. Aviators flying trailing aircraft may encounter wake turbulence (section V) if they permit their aircraft to go below leading aircraft. Flight in turbulence may result in rapid attitude (pitch, roll, and yaw) changes.
6-35. Distance between aircraft can be increased or decreased to fit the tactical situation. At terrain flight altitudes, aircraft may spread out to take advantage of the terrain/tactical situation. In addition, it is less fatiguing to fly loose or extended formations as opposed to tight or close formations.
6-36. All aircraft should have the P navigating in the event they must take over the lead position and assist the flight with ensuring navigational accuracy to complete the mission.
6-37. Altitude and airspeed changes should be smooth and gradual especially during tight and close formations. This allows all aircraft in the formation to act in unison. Abrupt changes in altitude and airspeed by the lead aircraft may cause an "accordion" effect. This results when all remaining aircraft in the formation make correspondingly abrupt altitude and airspeed changes to maintain their relative position, and the effects are magnified as the flight progresses. When flown incorrectly, aircraft toward the rear of a formation may experience excessive rates of closure as they attempt to maintain their relative positions.
FORMATION TURNS
6-38. The lead aircraft should make smooth constant rate turns and avoid angles of bank greater than 30 degrees. Turns at reduced bank angles require larger turning radiuses, particularly in the landing pattern, and must be considered in planning. If a large turn is required, flight lead enters the turn as early as possible to avoid excessive bank angles and subsequent recovery. This allows the flight to react in a timely manner. During a turn, the inside aircraft must decelerate slightly and drop slightly lower than the leading aircraft, while the outside aircraft must accelerate slightly and climb slightly to maintain its position in the formation. Whenever possible, the aviator avoids turns in which aircraft are forced inside the lead aircraft's turning arc. This is usually addressed during the planning process and briefed accordingly. Aircrews should avoid planning route segments requiring heading changes of more than 60 degrees.
FORMATION CHANGES DURING EN ROUTE FLIGHT
6-39. Formation changes en route require a high degree of proficiency and therefore are executed with caution and only when necessary. Any changes to a formation are specifically briefed and understood by all aircrews involved. As a technique, trail formation could be used as a transitional formation before executing the next briefed formation.
LEAD CHANGES
6-40. Lead changes are inherently difficult, potentially dangerous, and should be executed on the ground, whenever possible. A lead change is never initiated, day or night, by accelerating to overtake the lead aircraft. Only the lead aircraft may give the signal to initiate lead changes. Flight lead initiates by a prearranged signal, and the flight acknowledges beginning with chalk 2. The lead aircraft then makes a 30- to 90-degree heading change in the prebriefed direction to depart the formation and establish separation space. Lead maneuvers a minimum of eight rotor disks to the announced side and begins to parallel the formation. When chalk 2 (the new lead) confirms and announces the former lead is clear of the flight, the former lead will slow to 10 KIAS less than the en route airspeed. The former lead visually (and possibly verbally) confirms each aircraft in the flight as it passes to prevent rejoining the flight prematurely causing a midair collision. After the last aircraft (former trail) has passed by, the former lead aircraft will rejoin the flight and assume the duties of the trail aircraft to include displaying appropriate lighting. The former trail aircraft then reconfigures its lighting to conform to the rest of the formation.
FORMATION LANDING
6-41. All aircraft touch down at the same time while maintaining their relative positions within the flight. The rate of closure throughout approach and landing is somewhat slower at night than during the day. Flight lead should maintain straight-and-level flight until the desired approach angle is intercepted. Lead then maintains a constant approach angle and, where terrain and obstacles permit, makes the approach to the ground avoiding hovering turbulence and brownout or whiteout conditions. If the rate of closure is too fast, the aviator should avoid S-turns to lose airspeed. Instead, execute a go-around if unable to slow to the appropriate airspeed, especially with heavily loaded aircraft.
6-42. Lead must plan to touch down far enough forward in the PZ/LZ to provide sufficient landing space for the entire flight. When planning the touchdown, consideration should be given to obstacles and power availability on the departure. If potential whiteout or brownout conditions exist, the flight may have to spread out to the briefed landing disk separation before the approach is established facilitating safe landing conditions. The AMC should consider, based on aviator experience and the environment, stacking down and landing in reverse chalk order once flight lead initiates an approach. This reduces the possibility of being caught in the cloud from the preceding aircraft and is especially true with CH-47s when executing formation flight approaches to a snow field where potential exists for sliding after touchdown. Finally, if safety is in doubt regarding landing or landing conditions, the flight lead should execute a go-around. The go-around should be executed prior to descending below any obstacles or losing ETL to prevent sudden high power demands on the other aircraft.

https://rdl.train.army.mil/catalog/...ABC8718F9760-1274574464617/3-04.203/chap6.htm
 
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Sridhar

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The IAF has ordered a court of inquiry to establish the cause of such an "unusual" mid-air collision which claimed the lives of three wing commanders, a squadron leader, a flying officer and four personnel below officer rank.

The court of inquiry will ascertain if the pilots violated the standard operating procedures (SOP). Prima facie, it appears that both the helicopters were not maintaining the required distance while carrying out such drills. "Normally the distance between two helicopters is about 60 metres when they take off simultaneously or are flying in close formation. The investigation will find out if there was any deviation from the SOP or a case of cockpit indiscipline," a senior IAF official said.

Two MI-17 choppers collide, nine dead - India - DNA
 

Ray

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Apart from pilot error, it could also be due to wind and turbulence.

It could be because of Wind shear and turbulence.

One could read this link, especially the technical minded:

Wind shear and turbulence
Safety: wind shear and turbulence
 

Ray

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The video shows the accident is in a built up area.

It is supposed to have happened in an area where there is a field firing range.
 

Kunal Biswas

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The video shows the accident is in a built up area.
Sir, video of those helos are not MI-17 but Sea Kings, Not Indian..

 
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Kunal Biswas

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Nine killed in India helicopter collision.Two Indian air force helicopters have collided in mid-air in India's western state of Gujarat, killing nine defence personnel, air force officials say.The MI-17 helicopters crashed into each other just after take off from an air base near the village of Sarmat in Jamnagar district.Officials said the helicopters were on a training sortie.

Air force, police and fire brigade teams have reached the site of the crash and are assessing the situation.An air force spokesman in the capital, Delhi, said a court of inquiry had been ordered to determine the reasons behind the crash, the Press Trust of India news agency reported.
 
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venkat

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I was wondering why a video was being taken....may be somebody through a cell phone....finally the video doesn't belong the mi-17 crash...could it be one of the choppers rotor blades hit the other chopper due to formation flying? Tragedy could have been averted...As ray sir told could be due to wind shear and turbulence might have pushed one chopper uncontrollably towards the other. seashores are known to have unexpected wind turbulence...Quite sad!!!
 

pmaitra

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Two IAF helicopters crash midair in Gujarat, 9 killed - The Times of India

They are used for transportation of troops and also for bombing mission.
RIP. :(
Mil-17 is used for bombing missions, but it is not a 'bomber' helicopter. It was designed as a transport helicopter. It also not a multi-role helicopter, or it is a multi-role platform, with limited assault capabilities. ToI is not reporting properly.

Mil-24/35 is a multi-role helicopter.


Requiescite in pace

External stores are mounted on weapons racks on each side of the fuselage. The Mi-17 has six external hardpoints. The Mi-17 is provided with missiles, bombs, small arms and cannons.
Seems like large crews (4 - 5 each aircraft) for a bombing mission. Is that normal?
Those external loads are modifications, and beyond the scope of the original design decisions.

IAF likes to do this a lot. Many countries, including Russia, do this as well. IMHO, they really need to quit doing things with this helo that is it not designed to do.


Mil-17 with rocket pods in Kargil. One of them was shot down. Not very successful.

Same response. Modification possible, and popular, but a bad idea overall.

2-pilot+co-pilot
1-Navigator+Radio operator+gunner
1-weapon system operator+gunner
Nope. Two pilots, and one engineer. That's it. Rest are all troops (or supplies) for transportation.

I was wondering why a video was being taken....may be somebody through a cell phone....finally the video doesn't belong the mi-17 crash...could it be one of the choppers rotor blades hit the other chopper due to formation flying? Tragedy could have been averted...As ray sir told could be due to wind shear and turbulence might have pushed one chopper uncontrollably towards the other. seashores are known to have unexpected wind turbulence...Quite sad!!!
Turbulence. That is a possible cause. That is why they use Kamov-27 in many of our Navy Ships. Coaxial is the safer option.
 

Ray

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Most of the helicopter accident is caused by Turbulence

Wake Turbulence

Helicopters also produce wake turbulence. Helicopter wakes may be of significantly greater strength than those from a fixed wing aircraft of the same weight. The strongest wake can occur when the helicopter is operating at lower speeds (20 to 50 knots). Some mid-size or executive class helicopters produce wake as strong as that of heavier helicopters. This is because two blade main rotor systems, typical of lighter helicopters, produce stronger wake than rotor systems with more blades.



Example of wake turbulence


Wake turbulence is a natural by-product of powered flight, but was not generally regarded as a serious flight hazard until the late 1960s. Upsets or turbulence encounters associated with other aircraft were usually accredited to "propwash" and later on, with "jet wash."

"¢ The strength of the wake turbulence is governed by the weight, speed and wingspan of the generating aircraft.

"¢ The greatest strength occurs when the generating aircraft is heavy, at slow speed with a clean wing configuration.

It was never encountered at the same flight level as the generating aircraft or more than 900 feet below the generating aircraft. Therefore, a following aircraft could avoid the wake turbulence by flying above the flightpath of the leading aircraft

National Transportation Safety Board data show that between 1983 and 1993, there were at least 51 accidents and incidents in the United States that resulted from probable encounters with wake turbulence. In these 51 encounters, 27 occupants were killed, 8 were seriously injured, and 40 aircraft were substantially damaged or destroyed

The wake turbulence associated with helicopters also results from high pressure air on the lower surface of the rotor blades flowing around the tips to the lower pressure region above the rotor blades. A hovering helicopter generates downwash from its main rotor(s)

In forward flight a pair of downward spiraling vortices are shed from the rotor blades, This region of rotating air below the helicopter is where wake turbulence occurs.

Various sources to include:
http://www.faa.gov/training_testing/training/media/wake/04SEC2.PDF
 
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