Arrow Air flight 1285: icing or explosion?
On the 12th of December 1985, a DC-8 Jetliner operating as Arrow Air flight 1285 crashed on departure from Gander, Canada. This was an international charter flight carrying US troops from Cairo, Egypt to their home base of Fort Campbell, Kentucky, with stops to refuel at Cologne in West Germany and at Gander.
The flight departed Cairo on Wednesday at 20:35 and arrived in Cologne five hours later. They departed Cologne on schedule and the six-hour flight to Gander was without incident. They refuelled at Gander and left just over an hour later, at 10:15 UTC but early morning local time; it was still dark.
There were three flight crew (Captain, FO, flight engineer), five cabin crew and 248 passengers, most of them from the 101st airborne division on their way home. The mood must have been jubilant. It was just a few weeks before Christmas and the 101st airborne division had just finished a six-month deployment in Sinai on a peacekeeping mission. The weather at Gander was light freezing drizzle with snow. Another aircraft which departed that same morning requested de-icing but after the flight engineer did a walk-around, the DC-8 crew didn’t seem to think it was necessary.
It should have been a routine flight. But when the DC-8 lifted off from the runway, it seemed to struggle. It was travelling about 167 knots indicated airspeed when it rotated, which seems reasonable enough for a fully loaded aircraft at 500 feet elevation. Witnesses saw the DC-8 struggle to gain altitude. The airspeed increased to 172 knots but then it began to decrease again.
I wonder sometimes if the passengers noticed. Maybe not, although for the flight crew, it must of course have been immediately obvious that something was wrong.
The DC-8 flew low over the highway, close enough that two truckers said the lights lit up the cabs of their trucks. Some said they that the aircraft was in a slight right bank. Three witnesses reported seeing a bright glow from the aircraft; two of them thought it might have been a fire, although the third wondered if it was the runway lights reflecting off the aircraft.
The nose pitched up, likely a last desperate effort to get the aircraft to climb away from the terrain. But the aircraft continued to descend. It crashed into the trees about half a mile past the end of the runway and skidded for 300 yards through the forest before exploding as it struck an unoccupied building. The fuel in the fully-laden wing tanks burnt furiously. There was no chance of escape, no chance of survival.
The investigating body was the Canadian Aviation Safety Board or CASB (the Canadian TSB was formed in 1990, in part in reaction to this case). The CASB had a pre-designated investigation response team, the Go-Team, which headed out to the site immediately. A crash site can quickly become compromised so it is urgent that the investigation get on site as quickly as possible. The Go-team is a collection of experts, ranging from engines to aircraft structure to data collection from the FDR and CVR. Their first job is to secure the wreckage and collect as much information as possible.
When they got to the site, they searched the runway and the highway, looking for any components or debris from the plane, which could help them to isolate a mechanical failure. They also looked for marks on the runway to see if perhaps the tail had touched the runway during take-off. There was nothing.
It was snowing and soon the entire crash site was blanketed with snow. The investigators had to remove key pieces of the wreckage in order to examine it and then return a second time to inspect the area when the weather was clear. On that second visit, they cleared the trees, melted the snow and documented the crash site as best they could. This time they recovered all of the wreckage and moved it to a secure hangar at Gander Airport, laying it out on a grid pattern to match how it was found at the crash site.
The Flight Data Recorder on this aircraft was very basic and only recorded four parameters, none of which was useful in this case. It was scheduled to be replaced a few weeks later. The Cockpit Voice Recorder was also recovered but they discovered that it had not recorded anything to do with the flight, or indeed any of the previous legs. It had been out of order for some time but no one had noticed.
They searched for mechanical failing and structural issues, especially related to the engines and the hydraulics. They found no signs of mechanical failure before the impact; however there was so much damage, it was hard to be sure. The instruments were completely destroyed and could not be read and they had no idea which warning lights might have been lit before the aircraft began to impact the trees: one master fire warning bulb was off but it was impossible to tell the status of the second one. One of the engines Fire Warning Light was off but the other three? They couldn’t tell.
A French news agency in Beirut received an phone call on the day of the crash, in which an anonymous caller said that the Islamic Jihad claimed responsibility for bombing the aircraft. Islamic Jihad Organization was a Shia militia active in the 1980s who were demanding the departure of all Americans from Lebanon.
The terrorist group did carry out a number of bombings and other terror actions, including two car bombs at the US Embassy in Beirut. Every other attack that they had claimed was proven to have been caused by them. On the other hand, there was no record of any other aircraft which had been bombed by the group.
Investigators searched for signs of an explosion, including shrapnel which couldn’t be explained by the impact or other signs of a high-energy explosion. They also looked for signs of lacerations and burn marks in the clothing and luggage. The investigators found no clear evidence of a bomb but the wreckage of the aircraft was such that it couldn’t be dismissed either. The cockpit voice recorder might have easily solved this case, if it had been working.
There were mortars found in the wreckage, although it seemed unlikely that one might have gone off accidentally without any of the witnesses noting the explosion. There was evidence in other flights around the same time that military personnel were carrying dangerous equipment in their cargo, such as flares and explosives. It was against regulations, of course, but it happened. So it is possible, even likely, that there were smaller explosive items in the baggage which could have caused a small explosion or a fire without any help from terrorists at all. Again, with no cockpit voice recorder, there’s no way to know what the flight crew experienced in the final moments before they crashed.
At the time, there had been a few crashes which were demonstrated as the result of icing, however pilots still didn’t truly understand the impact of ice on the wings, especially how ice on the leading edge would affect the flight profile. During take-off and climb-out, the aircraft is at a low altitude and a high angle of attack, near maximum thrust and at high drag. It is a challenging phase of flight but in a “clean” aircraft, it’s not an issue. But it only takes a very light layer of ice to push the aircraft to the edge of the flight envelope. Rough ice, which is what was suspected in this case, has an especially large effect.
Especially if the aircraft is overweight.
Arrow Air worked out the weight using standard estimates, as do most commercial passenger flights: you may weigh your luggage when you check in but you rarely have to stand on a scale yourself; airlines have standard figures for passenger weights which they use to estimate the total passenger weight. Some will be over and some will be under but the idea is that it ends up about right.
Arrow Air had a standard “winter weight” of 170 pounds per person, 77 kilos, which included the person, their clothes and five pounds of carry-on baggage. This figure was used by the first flight crew, who flew from Cairo to Cologne, when they were working out the take-off weight. They found that they couldn’t carry all of the cargo and ended up leaving 41 duffle bags behind, might to the consternation of the military personnel.
At Cologne there was no change in passengers or cargo, so all that the second flight crew had to do was modify the fuel weight, which the first officer did. But later, that flight crew said that when they reckoned that the take-off weight was quite a bit heavier than what it said on the load sheet — around 10,000 pounds heavier. They increased the take-off reference speed to account for this, so that they were travelling faster at the point when they rotated (increasing the pitch angle to lift off) which gave them better performance in the initial climb.
But neither of them thought to mention this to the next flight crew, who took over the flight at Gander. In Cologne with a clean aircraft, a bit of extra weight may not have been a big deal and was easily dealt with by lifting off at a faster speed. But in Gander, with ice on the wing and not quite so much runway to play with, it could have caused the aircraft to lift off without being able to climb away safely.
Investigators attempted to recreate the actual weight on board. They concluded that the average weight per passenger was 164 pounds… but that was not counting their uniforms and their weapons. Some also carried extra clothes and souveniers with them on board. In addition to that was the carry-on baggage, which had caused the cabin crew concern when the troops had boarded at Cairo. This “carry-on luggage” had filled the baggage holds of the two 737 which had brought the troops to Cairo. The true average weight of these passengers, including their clothes and equipment and carry-on luggage, was closer to 220 pounds per passenger.
Also, the cargo weight as logged for the flights to Cairo was about 4,000 pounds heavier than was listed on the load for the departing flight. Even taking into account the 41 duffle bags left behind, it seems that the cargo was some thousand pounds heavier than used for the calculations.
In addition, the basic weight of the aircraft, which should be a set figure that the crew can rely on, was not correct. The aircraft weight didn’t include removeable equipment, which included pillows, blankets, drinking water or even galley equipment. The basic weight was actually another thousand pounds more than had been listed.
Once the investigators had corrected for all of these issues, they found that the take-off weight had been under-estimated by 14,000 pounds.
The ZFW (zero fuel weight) of the aircraft was in reality just four hundred pounds under the maximum authorised weight. Once fueled, the aircraft exceeded the authorised take-off weight by 8,000 pounds.
The Canadian Aviation Safety Board released a final report but the nine board members could not agree on the cause. Five of the board members believed that the rain and freezing temperatures had allowed rough ice to form on the aircraft’s wings.
The Canadian Aviation Safety Board was unable to determine the exact sequence of events which led to this accident. The Board believes, however, that the weight of evidence supports the conclusion that, shortly after lift-off, the aircraft experienced an increase in drag and reduction in lift which resulted in a stall at low altitude from which recovery was not possible. The most probable cause of the stall was determined to be ice contamination on the leading edge and upper surface of the wing. Other possible factors such as a loss of thrust from the number four engine and inappropriate take-off reference speeds may have compounded the effects of the contamination.
However, the other four published a dissenting opinion, arguing that there was no evidence to show that there was ice on the wing and that it was more likely that the aircraft was brought down by an in-flight fire.
In our judgement, the wings of the Arrow Air DC-8 were not contaminated by ice — certainly not enough for ice contamination to be a factor in this accident. The aircraft’s trajectory and performance differed markedly from that which could plausibly result from ice contamination. The aircraft did not stall. Accordingly, we cannot agree — indeed, we categorically disagree — with the majority findings.
The evidence shows that the Arrow Air DC-8 suffered an on-board fire and a massive loss of power before it crashed. But, we could not establish a direct link between the fire and the loss of power. The fire may have been associated with an in-flight detonation from an explosive or incendiary device. Consequential damage to various systems precipitated the crash.
The minority report cites the two witnesses who described bright yellow/orange glow as the aircraft passed over the highway, which the majority report didn’t mention, only quoting the witness who thought it was a reflection of runway lights. Neither report actually documented all three witnesses, only the ones that fitted their conclusion.
A scan of the full report, including the dissenting opinion, can be found here: http://flightopsresearch.org/data/files/arrow1285.pdf.
At the time, he Canadian Aviation Safety Board (CASB) was a new organisation, created in 1984 as an independent accident investigation board to replace Transport Canada’s Aircraft Accident Investigation Branch. It was modelled on the National Transportation Safety Board in the United States. This new board, still a part of Transport Canada, would investigate situations it felt were potentially hazardous and, where appropriate, make safety recommendations. These recommendations were not binding for Transport Canada to respond to.
The split vote in Gander showed the CASB in a bad light, especially when a judge in 1989 stated that he didn’t think either argument had any merit. He determined that neither conclusion was sound. The Canadian Aviation Safety Board lost the faith of the public and, in 1990, the Canadian Transportation Safety Board was formed. It was focused on all types of transport safety (railway, marine and pipeline) and was designed to be truly independent from federal departments and agencies. Its only goal was (and is) to advance transportation safety.
Meanwhile, thirty-five years later, the cause of the crash of Arrow Air flight 1285 is still unknown.