The novel Coronavirus, which originated from Wuhan, China has brought unmitigated disaster across the world. The disruptions it has caused to world order is unprecedented.
Consider this. Indian railways, since the first train rolled in 1853 from Mumbai (Then Bombay) to Thane, had stopped its regular service only twice in the history and that too for a day only. Once during WW II and the other one being on the day of Gandhi’s assassination. Today is the 61st day since Indian Railways stopped its passenger service countrywide. As the threat from the virus grew, India took some drastic and hard measures to stop the spread of the virus. On 24th March, India stopped all international and domestic operations of flights across India. As the lockdown is being eased gradually after 2 months, India is opening its skies again on 25th May for domestic operation to resume.
Never before in aviation history, such large fleet of aircrafts were out of service for 2 months before being brought into service again. It raises several eyebrows on safety of flight operations and airworthiness of the aircrafts. Of course, there are SOPs for airplanes returning to service after extended downtime, but it has never been carried out on such massive scale ever.
Inspection of aircraft for airworthiness
Aircrafts do go through scheduled maintenance and periodic inspections to certify the airworthiness. These are categorised as A, B, C and D check which are carried out as per time intervals or flying hours. While A, B and C can be carried out in the hangar itself, D check which is most extensive, is often carried out at a manufacturer’s facility. These checks often include
- Visual inspection of aircraft parts
- Hydraulic fluid levels
- Lubrication of moving parts
- Engine functions
- RAT deployment
- Landing Gear functions
- Cabin pressurisation system
- Hydraulic actuators
These checks are performed in regular time intervals. However, these are scheduled maintenance checks aimed at servicing parts that may suffer wear and tear during regular flying. Extended parking may cause deterioration of non moving objects, which are vital in flight operation and may not be included in the scheduled maintenance. This mostly includes the aircraft surface, various sensors exposed to weather, physical structure etc. Hence a SOP for getting planes back into service after extended downtime is essential. Boeing and Airbus manuals have specific extensive chapters dedicated to “Maintenance practices for extended parking”.
The parts that are most vulnerable to airplane inactivity are the ones exposed to weather. A bit on those before we proceed.
Pitot Tube – This is an instrument used to measure airspeed. Airspeed is the speed an aircraft achieves using engine power. Imagine a car moving at higher speed than the engine power applied when going downhill and lower speed when going uphill. Uphill is headwinds and downhill is tailwinds in aviation. Air speed +/- Wind speed is the ground speed or actual speed of the aircraft. The pitot tube probe is generally placed alongside the fuselage of the aircraft with 2 holes in it.
Static Ports – This measures the ambient air pressure of the outside air. The output from this instrument is used by Altimeter, Cabin Pressurization system, Vertical Speed Indicator and Airspeed indicator. It works along with pitot tube and together it’s known as pitot-static system.
Angle of Attack (AoA) Sensor – As the name suggests, this tells the angle of oncoming air relative to aircraft’s wing (Or a reference line along the wings). Described in more detail in our article on the Boeing 737 MAX.
All these sensors are exposed outside the fuselage and are prone to vagaries of weather. The 2 accidents involving aircrafts returning to service after extended parking involved blocked pitot tube probe and static port contamination.
We have already seen how a faulty AoA sensor had taken down 2 brand new Boeing 737 Max and the entire fleet across the world had to be grounded and continues to do so. The inputs from all the 3 are extremely vital to aircraft operations are they are fed to onboard flight computers who then take important decisions. A wrong input may have catastrophic consequences as we have seen in the past.
Hence, along with the schedule A, B or C check as applicable, the aircrafts do go through extra set of checks before returning to service. Apart from these, there are other parts which may have been affected during extended parking. Lubrications in moving parts, batteries getting discharged, fuel tank or fuel pipe contamination (due to insects or impurities getting stuck), tyres, hydraulics are some of the other parts that are included in SOP for aircraft returning to service. Engine, APUs and fire extinguisher systems are anyways regularly serviced to maintain the airworthiness.
The routine preflight checks are performed before taking to the sky includes a walk around, switches, circuit breakers, hydraulics, brakes, radios, transponders, fuel systems, trims, rudder function, flaps, slats among others. Airlines make the air worthiness of an aircraft absolutely sure before allowing it to take to the sky.
There are some apprehensions among passengers after the recent PIA A320 crash in Karachi yesterday. However, it is would be hasty to comment because we don’t know if the aircraft was parked for a long time or was it commencing regular service. Also, from the radio comms between the pilots and ATC, it’s clear that the pilots lost both engines. It’s premature but unlikely that this would have been caused due to prolonged parking. Let’s not speculate about the incident till an investigation report comes to fore.
The engineering staffs on the ground and the pilots along with the crew in the air will make sure we will have a safe flight as the aircrafts take to Indian skies after 2 months break. Let’s put our apprehensions to rest and look forward to the beautiful giant metal birds roaring into the Blue skies with all their glory.