Many of you probably know what happened to Boeing 737 MAX. By the beginning of 2021, its drawbacks that had led to two catastrophes with human victims have been identified and repaired. This airplane model has begun to be progressively returned into operation. But then, suddenly, on April 9, 2021, Boeing issued an order for the companies operating 737 MAX to inspect airplanes for "sufficient grounding ways for power supply system elements." This order covers not all Boeing 737 MAX but only those with particular serial numbers.
The need for a new airplane check created significant problems for several carriers. For example, American low-cost airline SouthWest Airlines had to check 30 out of its 58 airplanes of this model.
This story has become a reason for social media to begin discussion on "Why does an airplane need grounding?"
Grounding is certainly necessary for an airplane landed on the ground. The sooner the airplane's body is connected to the grounding after landing, the better. One of the reasons for this is a difference between physical effects of lightning on airplane in air and on the ground.
Modern aircrafts are designed to be able to withstand a lightning strike in the air. When the lightning strikes, the current of about 10 kA flows through an aircraft. But it flows along multiple ways. Due to this, the resistance to lightning current is about 0.001 Ohm (for a whole-metal plane). Therefore, potential difference between the lightning current inlet and outlet is about 10 V.
When an airplane is on the ground, the lightning current flows freely through the body and gets into chassis supports. Voltage of many million volt and more leads to an electrical breakthrough in rubber tyres. This, in its turn, leads to tyre damage, smoke or even fire.
The airport's technical service personnel connect the airplane's body to the grounding. Moreover, power supply and air conditioning plants are also connected to the grounding using separate wires. The availability of a separate connection to the grounding for these assemblies is related to the need to prevent sparking due to appearance of static electricity during the airplane fuelling.
Grounding systems in aviation are an important factor of flight safety. Section lightning protection and grounding design examples at our website contains a flying line grounding design, which can help understand a typical solution to create a grounding arrangement for the airplane parking space. If required, the ZANDZ Technical Center engineers will make for you the calculation for the grounding which takes into account all specifics of a particular airport or site. You can just send a technical request and your wishes to us. You can read a large article written by Prof. E.M. Bazelyan to learn more about the lightning protection for airplanes.