Lessons from the past
An ATSB Final Report (AO-2012-137) has recently been published on the Fokker 100 hard landing at Nifty WA in 2012. It makes scary reading that a sudden and completely unexpected micro-burst a few seconds before touch down caused the airspeed to drop 23 knots in three seconds between 30 and 80 feet agl. No wonder the aircraft fell out of the sky resulting in a hard touch-down.
Just yesterday I discovered in my shed, DCA Aviation Safety Digest No 1 dated July 1953. The original DCA “Crash Comic.” It was in good nick so I took it to my local coffee shop and read it. The magazine had 27 Pages of first class reading. No advertisements and no quizzes. Part 1 included aviation news and views (in other words good gen such as cockpit design and safety, refuelling dangers, how long does it take to feather manually and starting accidents) Part 2 Overseas Accidents. Part 3 Australian accidents. Part 4 Incident reports.
Page 24 discussed a take off accident to a DH89 Dragon Rapide, a twin engine biplane first flown in 1930. The ASD summary said “During the take-off run at Hookers Creek, Northern Territory, the pilot of a DH.89 decided to abandon the take-off owing to a violent change of wind. The aircraft over-ran the end of the strip and ran into partially cleared scrub. The aircraft was extensively damaged, but neither the pilot nor the two passengers were injured. The single strip is 3,200 feet long.
The pilot had landed at Hookers Creek without incident, although he noticed a deterioration in weather was imminent. Two passengers and some mail were taken aboard and preparations were made to take off in the 098 degree direction of the landing strip. When half the take-off run had been completed and before the aircraft was airborne a violent swing of wind to 300 degrees occurred. This resulted in a tail wind component estimated at 50 m.p.h. The pilot, sensing that he was covering too much ground before obtaining flying speed, decided to abandon the take-off when two-thirds of the strip had been covered without becoming airborne. Despite the remaining uphill slope and the application of brake, the aircraft, helped with by a strong tail wind, continued beyond the end of the strip where it collided with scrub before being brought to a halt.
Conditions of violent wind changes are well known in this locality, but as local weather information is dependent largely on voluntary reports from stations, wind changes cannot be easily forecast. A more careful judgement of weather conditions may have shown that adverse wind conditions could be expected at or about the time of take-off. The cause of the accident was a sudden and violent change in wind velocity which the pilot did not anticipate.
The term micro-burst was unknown in those days but reading that 1953 ASD report brought back memories of my own experiences of wind-shear. In November1953 I was tasked by the RAAF to take a Dr Gavin Douglas in a Wirraway from Townsville to Hughenden. A station hand had been badly burned in a fire and needed urgent medical attention. The forecast for the flight was fine. With the doctor in the back seat we departed Townsville to the west and arrived at Hughenden 1.5 hours later. The doctor said he would be back at the airport within three hours providing there were no complications with the patient. It was mighty hot as the afternoon wore on and I was concerned at the approach of a low dark cloud from the west.
There were no flares at Hughenden and I was anxious to get back to Townsville before last light. The wind sock was slack when the doctor arrived in a cloud of dust back at the airstrip and as I helped him into his parachute into the rear cockpit, the approaching dark cloud was a mile or so from the airport. The take off direction was away from the cloud and after a quick magneto check I started the take off. There were the usual trees and scrub surrounding country airports and I realised the airspeed was awfully slow to increase and the far trees were getting close. I had a quick glance at a nearby windsock and was shocked to see it standing nearly horizontal at about a 20 knot tail-wind. Yet another wind-sock at the beginning of the runway had been quite limp. A micro-burst or just a wind-shear from a fast moving front? I don’t know
Either way, it was too late to abort so I fire-walled the engine and just got airborne by the runway end. The trees were higher than I expected and I dropped down a few degrees of flap and cleared them by a few feet and still just above the stall. Eventually I was able to accelerate, retract the flaps and set course for Townsville. The doctor in the back seat was restricted in forward vision by the front cockpit which was probably just as well. After we arrived at Townsville I told him what had happened. He was not concerned. Some 10 years later my wife was in a Melbourne hospital for treatment. By amazing coincidence Dr Douglas was her surgeon.
We have seen what happened to the Fokker 100 when it was hit by a micro-burst at Nifty. The DH.89 Dragon copped it on his take off run and so did I in the Wirraway. In each of the three instances the wind shear caught the pilots by surprise. Another type of wind-shear was nearly a disaster for a Boeing 737 pilot landing at the United States Navy base at Guam in the Marianna Islands. The airport called Agana, has two parallel runways. Runway 6L is 10,000 feet long with an ILS and Runway 6R 8000 ft with no navaids or VASIS. A single taxi way adjoins the threshold of both runways and back tracking is required to reach the starting points of 6L and 6R. The two runways are about 200 metres apart Sometimes ATC will require an aircraft on mid final 6L ILS to break right (called side-stepping) and align to land on 6R. An aircraft at the holding point on the taxi way joining the runways will then be cleared to line up and depart on 6L while the aircraft on final will land 6R. Usually everything goes smoothly but this time it didn’t.
The arriving Air Nauru Boeing 737-200 was on the ILS having arrived from Manila. ATC instructed the aircraft to break right and side step right to land 6R when visual. Meanwhile a Pan American Airways Boeing 747 was holding short of 6L, on the threshold taxiway between the two runways, awaiting take off clearance. The night was dark and wind calm.
The 737 reported visual at four miles on ILS final and turned slightly right to align with 6R. Soon after, ATC cleared the waiting 747 to taxi from the holding point for 6L and to take off 6L. The pilot of the 747 acknowledged the instruction. At 500 feet on short final for 6R, the crew of the 737 were slightly high on glide slope because there was no VASIS on 6R. As the 737 passed over the threshold of 6R at Vref speed of 134 knots, the captain who was PF, felt the wings rock sharply and at the same time the aircraft appeared to drop out of control. The startled first officer called out loudly “VREF minus 20”. Fortunately the captain had already started to go around by pulling back hard on the control column and pushing the thrust levers to the forward stops.
Just as the aircraft was about to hit the runway, the thrust took effect and the 737 climbed away without further drama, apart from the fright experienced by the crew. It quickly entered cloud, the clean up of flaps and gear commenced, and the aircraft was radar vectored for the 6L ILS. That landing was uneventful.
It transpired that the Panam 747 did not line up immediately after being cleared for take off by ATC. This meant it stayed in position on the taxiway with the tail of the 747 at right angles to Runway6R and some 50 -75 metres from 6R. The pilot of the 747 then chose the wrong moment to open his thrust levers to break-away thrust, just as the Air Nauru 737 passed directly behind and across the jet efflux of four engines. . Because it was night it is possible he failed to see the 737 on short final and behind him. The jet blast and heat effect hit the 737 as it came through slightly above the glide slope. The dramatic loss in airspeed then took place. It was indeed fortunate that the 737 was higher than normal over the 6R threshold due to no glide slope guidance, otherwise the result could have been very serious.
It goes to show that no matter how experienced the pilot is – both the Fokker 100 crew and the 737 crew were highly experienced – wind-shear from whatever source can be dangerous especially if there is no prior warning. While the Fokker crew had practice at wind-shear recovery during cyclic training that could have been three years apart; which is not exactly current training. .