On Sunday, 30 June 2019, a light helicopter (appears to be a single-engine Bell 407), carrying Mahant Balaknath, the BJP MP from Alwar, appeared to go out of control for several seconds, while attempting to land at a helipad in Kotkasim area, 190 kms from Jaipur, Rajasthan.
As per amateur footage released by ANI on Twitter, the helicopter is seen making a normal approach to land. During the transition to hover, it starts to spin to the right. In a tightening spiral, the helicopter does at least four to five 360-degree turns before arresting the turn and finally flying away.
By all indications, the helicopter was not chartered for aerobatic display, so something unusual has happened. As per reports, the pilot aborted the attempt to land and returned to Delhi from where the MP left for his destination by road. Thankfully, nobody was injured.
Before we beat up a hysteria and invoke gods and goddesses, take a moment to understand what may have happened. The ‘seconds from disaster’ experience can be unpacked into the few ‘probable causes’. For those interested in a deeper understanding of the topic, my essay on the complete spectrum of ‘Tail Rotor Troubles’ can be read here.
So Much Trouble Just to Keep the Nose Straight?
The tail rotor (TR) in a conventional helicopter is meant to counter the tendency of fuselage to rotate in the opposite direction to that of the main rotor, due to Newton’s Third Law of Motion. So, for every power setting, there is requirement for a certain ‘tail rotor trim thrust’ to keep the nose-pointing in the direction of flight. Above and below this ‘trim thrust’ or ‘rudder trim’, the helicopter will start to rotate – either away from the spinning main rotor (due insufficient TR trim thrust), or in the same direction as the main rotor (when TR thrust is in excess to trim thrust).
Loss of Tail Rotor Effectiveness (LTE)
When any helicopter transitions from forward flight to a hover, like it did in this case, there is a gradual increase in power application. Hence, there would be a proportionate increase in TR trim thrust. If this control input is insufficient or degraded due to external factors like high altitude, adverse winds, high temperatures, or due to handling deficiencies, the helicopter can quickly spin out of control.
Such a phenomenon is called ‘loss of tail rotor effectiveness’ or ‘LTE’, in the helicopter world.
LTE is an ‘uncommanded', rapid yaw rate, happens only at low speeds and only in the direction away from main rotor rotation (to the right for a Bell 407, as evident in the video).
Helicopter pilots juggle with numerous internal and external factors while operating from unprepared areas. Hazardous conditions always exist in a helicopter pilot's 'uncontrolled' environment. Awareness about LTE, height and speed are key factors in prevention and recovery.
The best remedy for LTE is to not set up for one. If you still encounter one, pilots are advised to apply full opposite rudder, and if possible, lower the power setting.
Balaknath’s helicopter however did not have this luxury, being close to the ground. Putting down a rapidly-spinning helicopter will surely break the machine (and some bones).
Freak cases where a passenger or crew member managed to get the rudder pedals stuck by putting their foot in the wrong place, have also been documented!
Heatwave Affects Helicopters Too
Helicopters and aeroplanes with air-breathing turbine engines, are as susceptible to heatwave conditions as humans. A higher temperature means lower air density, which the helicopter engine sees as an increase in virtual altitude (also known as density altitude). Just as humans would experience a depletion in their capacity to work with increasing temperature, so would aero engines.
Alwar in Rajasthan, sees extreme temperatures in late June. Surface heating can cause ‘heat lows’ or local low pressure areas, giving rise to gusty winds.
A combination of adverse wind conditions coupled with high temperature and high loading, can set up an invisible trap that may become evident only after getting into it, even while operating within the aircraft’s approved envelope.
Dust bowls kicked up during landing can blind the crew, even leading to loss of control.
DGCA norms stipulate a host of criteria and a state of preparation for such temporary helipads. This includes the provision of a windsock or some arrangement to indicate wind direction, two-way radio, local weather updates etc. Were these criteria observed in letter and spirit, only people involved in this incident will know. Like they say, “yeh andar ka mamla hai!”
Half Begun, But Well Done!
To the credit of the pilot, he managed to recover the helicopter from a very precarious situation without losing his head. The high rate of rotation can be disorienting, and can also cause cross-coupled motions in other axes. Baggage and pax not buckled down firmly can be thrown about, causing secondary effects. Even if he was caught unawares, subsequent actions were appropriate in my estimate. Much to be learnt, for every helicopter pilot, from this episode.
And yes, heatwave conditions are very much applicable to machines as they are to humans.
So to those who were clapping at the spinning helicopter, remember to send out a few rounds of applause for the pilot who saved the day for Mahant Balaknath. This is my ‘mann ki baat’ for you!
Happy landings! Remember to drink lot of water. And whether in politics or flying, always keep your tail clear.
(Capt KP Sanjeev Kumar is a former navy test pilot and blogs at www.kaypius.com. He can be reached at @realkaypius. He has flown over 24 types of fixed and rotary wing aircraft and holds a dual ATP rating on the Bell 412 and AW139 helicopters. This is an opinion piece. The views expressed above are the author’s own. The Quint neither endorses nor is responsible for them.)
(At The Quint, we question everything. Play an active role in shaping our journalism by becoming a member today.)