On Sunday, 30th Jun 2019, a light helicopter (appears to be a single-engine Bell 407) carrying BJP Member of Parliament from Alwar, Mahant Balaknath, 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.
Since the helicopter was not chartered for aerobatic display, something unusual has definitely happened! As per reports, 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 & goddesses, take a moment to understand what may have happened. The ‘seconds from disaster’ experience can be unpacked into a few ‘probable causes’.
For those interested in a deeper understanding of the topic, my 3000-word 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. Anything less or more than this ‘trim thrust’ or ‘rudder trim’, the helicopter will start to rotate – either opposite to 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 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. It happens only at low speeds, only in the direction away from main rotor rotation (to the right for a Bell 407, as evident in the video).
Some pilots may argue that LTE should be called ‘loss of pilot effectiveness’. Well, jury is out on that one. Helicopter pilots juggle with numerous internal and external factors while operating from unprepared, often treacherous areas. Such 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 reduce the power setting. Balaknath’s helicopter however did not have this luxury, being close to ground. Putting down a rapidly spinning helicopter will surely break the machine (and some bones!).
Loss of Tail Rotor Control
In some cases, TR control may be lost, either partially or fully. In such a case, whenever the TR trim thrust exceeds the setting at which the tail rotor is stuck, control can be lost. Regaining control is a delicate manoeuvre and decidedly tough at low speeds and hover. This condition is also known as ‘stuck rudder’.
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!
Complete Loss of TR Drive
Complete loss of TR due to failure of the tail drive, TR impacting terrain or obstacles (tail strike) or for any other reason, can be disastrous if the pilot does not react immediately. Extremely high rate of turn can build up within seconds. Crew may be left with no option but to shut down the engine (s) and autorotate to the ground below. This was obviously not the case with the BJP MP’s helicopter which managed to fly away and land safely at Delhi.
‘Heatwave’ is also a ‘Precipitating’ Condition!
Helicopters and aeroplanes with air-breathing turbine engines are also susceptible to ‘heatwave’ conditions. A higher temperature means lower air density, which the helicopter engine sees as a virtual increase in altitude (also known as density altitude). Just as humans would experience a depletion in their capacity to work under heatwave conditions, so would aeroengines.
Alwar, Rajasthan, experiences extreme temperatures in late June. Surface heating can cause ‘heat lows’ or local low pressure areas with gusty winds. Adverse wind conditions at the helipad coupled with high temperature, high all-up weight (AUW), and poor anticipation of the combined ill-effects can set up a trap that may become evident only after getting into it, even while operating within the aircraft’s approved envelope.
DGCA norms stipulate a host of criteria and preparation for such temporary helipads. This includes provision of a windsock or some arrangement to indicate wind direction, basic first aid and firefighting, local weather updates etc. How many such criteria were observed in letter & spirit, only the people involved in this incident will know. Yeh andar ka mamla hai!
Half Begun, But Well Done!
To the pilot’s credit, he managed to recover the helicopter from a very precarious situation without losing his head. Rotational rate of approximately 90-degrees per second can be highly disorienting, with cross-coupled motions in other axes as well. 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 applicable to low flying machines as they are to man!
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! Whether in politics or flying, always keep your tail clear!
©KP Sanjeev Kumar, 2019. All rights reserved. An edited version of this story was first published by The Quint on 1st July 2019. You can access it here. Cover photo from Wikipedia (used for representation only).
Disclaimer: If you are a flight crew, please consult national regulations, the Rotorcraft Flight Manual or Aircraft Flight Manual and your company’s Operations Manual as applicable to the type you fly. Views are personal. I can be reached at firstname.lastname@example.org.