Rumblings of a Comet

Published On: February 23, 2019 01:30 AM NPT By: Hemant Arjyal

Comet-4 flew high over Kathmandu in 1959, during Prince Philip’s first ever India trip. It seems he wanted to have closer look at the Himalayas

No, it is not about A380 which happens to be top aviation news this week. A380 is a marvellous aircraft no doubt, but it not just had “too much wings” but also “two engines” too many. This time it is about another four engine passenger jet that was conceptualised and built soon after World War II. The long forgotten Comet (formally “DH.106 Comet 4”) was made by UK’s de Havilland. But it started to have serious issues as soon as it began flying passengers. Its pilots were not thoroughly attuned to high altitude, high speed flying; there was more to learn over time. 

Using unsafe products and following improper practices often lead to accidents. The Comet was seen to suffer on both accounts as serious accidents kept happening in quick successions. It was more due to ignorance as designers had no clue about manufacturing practice followed then, and it was also inherently flawed. In that respect, everyone of Comet’s flaw contributed in making aviation safer. Being the most daring venture of the time, it ended being not as successful aircraft as like others following it.  

Crashing cases 

The first Comet mishap occurred less than six months after it was put to commercial use. The Rome runway overrun (May, 1952) did not result in any fatalities but the same at Karachi (March, 1953) led to 11 deaths. The Calcutta accident (May, 1953) was the worst ever with 43 fatalities with aircraft having broken in midair. Another midair blow up, barely after eight months in January 1954 resulted in more fatalities (35) near Rome. The third, suspected blow up happened between Rome and Cairo (April 1954) as the aircraft was reported to be climbing to FL350 (35,000 feet) when it disappeared over the Mediterranean. Its wreckage remained untraced. 

With midair blow up happening despite improvements there was no option but to ground the fleet completely. A thorough crash probe was ordered since the prestige of UK aviation industry was at stake. Perhaps, no other accident had gone to this length in analysing the root cause of an air crash. As such, substantial portion of Comet’s fuselage and engine (January 1954 crash) were recovered from the depths of the Mediterranean to facilitate the post mortem. With the uncertainty continuing, the Comet not just lost confidence of the flying fraternity but also orders from airlines. 

As for its making, its outer metal skin was crudely “punched” and then riveted much like with other aircrafts of the period. Aircraft generally have too many closely spaced rivets on their exterior. If one tries to hammer a nail through a metal sheet it always ends making an untidy jagged puncture. As such, aircrafts had as many jagged holes under the skin as the rivets. Low flying (non-pressurised) aircraft had no issue even with this type of work practice. But it seriously conflicted with the safety of jets, because they needed to have pressurised cabins. With weakest point succumbing to repeated stress, the unseen fault line continued to spread further making it progressively weaker. Besides, it also had rectangular windows, a common practice again. But no one paid much attention to the sharp corners from where the cracks always started. This was more serious as a window is nothing but a big opening on the outer skin. That is not all. The problem was further compounded by the use of “thinner” outer skin sheet to reduce aircraft’s deadweight. Every Comet, built thus, got ominously closer to bursting with each cycle of operation. It was, virtually, a ticking time bomb.

It was irrevocably established that metal fatigue was the culprit in midair blow ups. It progresses very slowly and is not apparent unless very closely scrutinised. Subsequently, the fuselage skin was made thicker, cabin windows became oval and drilling superseded brute punching. There were no major issues thereafter. The rejuvenated Comet made a comeback but it was much too late in stopping Boeing707 which had already captured market for being more capable in terms of capacity and range.

Initiative for change 

The Comet did adopt innovative aspects of design namely, swept back wings, fuel tanks in the wings and main landing gear with four wheel bogies. Its turbojet engines came embedded in wings closer to the body making it aerodynamically better as it greatly helped to reduce drag. But Comet-4 could not proceed beyond Gander (Newfoundland), after crossing the Atlantic, without refuelling even if it carried no more than 106. Comet was naturally patronised by UK registered airlines like BOAC, BEA and Dan Air and also by RAF. In fact, Dan Air at its peak owned 49 Comet-4s. A total of 114 Comets got built including 37 of its early versions.  

Interestingly, there was one tiny incident which brought Comet-4 high over Kathmandu in 1959. This was during Prince Philip’s (Duke of Edinburgh) first ever India trip. It seems that he was flying from Calcutta to Delhi and wanted to have closer look at the Himalayas on the way. This was conveyed to Nepal authorities and this scribe happened to overhear Mr Biranchi Man Pradhan, the airport chief, talking about it at my relative’s place in Patandhoka. “Tomorrow at about eleven” said he, “it would pass over the valley”. 

The next day was as bright and blue as always, unlike what we have now and valley used to be far quieter as well. At around the given time we heard first a low rumbling noise coming from above. Then we had a clear sighting of an aircraft flying high from east to west disappearing away rumbling in no time. Though it was not much, it was naturally, an exciting and memorable incident for a ten year old.

Comet’s contribution to aviation safety and bold design innovations cannot ever be undermined. It was a no mean feat to have produced 77 Comet-4 frames despite early difficulties and continuous adversaries’ onslaught. Its passenger version was retired in March 1997 while the maritime variant flew until 2011. That was over six decades after first Comet flight in July, 1949.

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