Mumbai: Aircraft manufacturer Boeing recently issued airline-specific bulletins alerting pilots to a long list of possible problems the cockpit could be besieged with at lower altitudes if 5G signals from a transmission station near a US airport ever happen to hazardously interfere with those of an aircraft instrument that measures accurately the plane’s height over ground.
Air India, the only Indian carrier that flies to the US, operates the route with Boeing wide-body aircraft. Other aircraft manufacturers too have issued similar documents, but the 5G effects vary. For instance: Airbus document states: “On A350 and A380 aircraft, 5G interference on radio altimeters are negligible, hence the absence of cockpit effects.”
How do pilots read this?
A senior B777 commander said: “Boeing has listed everything that could possibly go wrong in the cockpit if 5G interference ever happens...The message pilots get is, don’t attempt low-visibility landings, the radio altimeter isn’t reliable. Also, when landing in good weather, stay extra alert after descending 2,500ft and be ready for a manual landing.”
Another senior Boeing 777 commander, who is from Indian Pilots’ Guild, the Air India union with B777 pilot-members, said: “Boeing has alerted pilots to the worst-case scenario. A Flight Crew Operations Manual is essentially a user-manual for an airplane. A bulletin is issued when a system might not function the way it is supposed to. When Boeing issues a bulletin, about 8 out of 10 pilots will never face any of the situations mentioned in it ever.”
What pilots concur is, with 5G rollout in the US, the workload in the cockpit of US-bound aircraft has gone up. For instance: at height below 2,500ft, pilots will now need to be alert for possible 5G interference. Boeing instructs them to monitor and cross-check between two different altimeter readings. Above 2,500ft, a barometric servo altimeter gives altitude information by reading atmospheric pressure differences. It’s not affected by 5G waves. Below 2,500ft, aircraft systems and pilots rely on the more accurate radio altimeter readings. But if 5G wave interference happens, the radio altimeter could fail or give erroneous readings, says the bulletin.
Capt Amit Singh, an air safety expert said: “At extremely low temperatures, barometric altimeter readings are not accurate. Now, the radio altimeter reading too is under suspicion because of possible 5G interference. So how can a cross-check happen between two sources that are not reliable?”
Low temperatures also can present low-visibility conditions which is when approach and landings such as CAT-III—‘blind’ landings done by depending on aircraft instruments and ground navigation aids—are carried out. A 5G wave interference could lead to erroneous radio altimeter readi-ngs being fed into aircraft systems. So the ‘autopilot’ functions that help carry out low-visibility landings could fail, said the bulletin. Warning syste-ms that alert pilots to other aircraft on collision course could fail. Systems that give alerts on approaching terrain, obstacle might be rendered inoperative or function erroneously.
Capt Singh said: “During training, pilots are drilled to trust the aircraft instruments to prevent spatial disorientation during low-visibility operations. With 5G, these instruments are under suspicion. Moreover, no specific set of instructions are given in the bulletin. From a human factor/performance perspective it’s a difficult task which will add to the workload and stress.”
Capt. Sam Thomas, president, Air Line Pilots’ Association (ALPA), India said :“The current Boeing bulletin lists a host of issues that can occur with various systems…What the pilots require are unambiguous information and clear cut risk mitigating procedures,” said Capt Thomas. “We at ALPA India believe that a detailed evidence based study needs to be carried out before a comprehensive commentary can be made. Prima Facie it (the Boeing bulletin) almost prevents operations into the said airports,” he added. “The radio altimeter is a very key component of the aircraft and almost all automation have some amount of dependency on it. Autoland functions cannot be carried out unless dual channel radio altimeter is functional. The current bulletin lists a host of issues that can occur with various systems which leads one to believe that operational safety is in question. What the pilots require are unambiguous information and clear cut risk mitigating procedures,” Capt Thomas added. “We at ALPA India would like to request pilots to exercise abundant caution while operating to the airports in the United States mentioned in the NOTAMS which are likely to have Interference with 5G spectrum bands,” he added.
24/01/22 Manju V/Times of India
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