In an airline you should have ground crew trained to determine if the aircraft is free of ice and pilots are more at less at the mercy of the ground crew. The same applies in the U.S. of commercial crews who have been trained under the provisions of 14 CFR 121.629(c) and 135.227(b). But all pilots should be wary of the effects of cold fuel in wet wings in conditions conducive to frost or icing, or even in conditions of high humidity. In these conditions, a de-ice treatment may not be good enough. You should consider an application of anti-icing as well as a pre-takeoff contamination check.
A noteworthy element to this accident was the presence of a third pilot in the cockpit to provide a calming influence and a third set of eyes to avoid mistakes. This off-duty pilot kept the PF focused on getting the airplane safely on the ground, remembered to get the flaps, and provided assurance that the gear should be extended for the crash landing.
[SHK Statens haverikommission Accident Report, p. 9] Weather. METAR Stockholm/Arlanda 0850 hrs: Wind 360° /11 kts, visibility > 10 km, light intermittent snowfall, cloud 2/8 stratus base 600 ft, 6/8 stratus base 800 ft, temp/dewpoint -0°C/-1 °C, QNH 1013 hPa, Sunrise 0848 hrs
[SHK Statens haverikommission Accident Report, ¶1.1]
- An aircraft of type DC-9-81 operated by Scandinavian Airlines System (SAS) and registered in Denmark with the markings OY-KHO landed at Stockholm/Arlanda Airport on 26 December, 1991, at 2209 hrs. It came from Zurich and had been flown at cruising altitudes at which the external air temperature varied between -53 and -62°C. The flight at these altitudes had lasted approx. 1 hour and 40 minutes. On landing there remained approx. 2,550 kg fuel in each wing tank.
- After landing the aircraft was parked at gate 2 at the international terminal. During the night a flight technician inspected the aircraft. He was compelled to clean slush from the landing gear to be able to inspect it. When he left the aircraft on 27 December at approx. 0200 hrs he noted that ice had formed on the upper surface of the wings. The air temperature had up to that point been + 1 °C.
- On the morning of 27 December the aircraft was to be flown to Copenhagen on SAS flight SK 751 with scheduled departure at 0830 hrs. The mechanic responsible for handing over the aircraft on the morning of 27 December noted at about 0730 hrs frost coverage on the underside of the wings. He therefore checked whether there was ice on the upper side of the left wing by climbing a ladder, putting one knee on the wing and feeling the forward part of the wing with his hand. He found no ice, but did find slush. Using a ladder he checked the air inlet of the left engine and found nothing abnormal. At 0650 the external air temperature had sunk to +0°C. At 0820 hrs an external air temperature of -0 ° C was recorded.
- The aircraft was fueled with 1,400 kg of fuel and was ready for de-icing at 0830 hrs. The mechanic had after consultation with the captain ordered de-icing of the underside of the wings also, because of the frost they had seen there. There had been no discussion of clear ice.
- During de-icing of the upper side of the wings the mechanic after a first spraying with de-icing fluid ordered further de-icing to make sure that the wings would be free of slush. For the de-icing a total of 850 I de-icing fluid type I was used. The temperature of the fluid was approx. 85°C. After de-icing the mechanic did not check whether there was any clear ice on the upper side of the wings, since he had previously found none.
- The person who operated the spray nozzle of the de-icing truck has stated that he saw that one of the four indication tufts fixed to the upper side of each wing moved during the spraying. A passenger who had been sitting in a window seat reported that the tufts on the wing he could see through the window did not move during the spraying.
In a classic sense, a "tuft" is a piece of string attached to the aircraft at one end and loose at the other to show relative airflow. I am looking for a photo of an MC-80 tuft, if you have one, please "contact Eddie" below. In the meantime, you can see one here: https://lessonslearned.faa.gov/ll_main.cfm?TabID=3&LLID=29&LLTypeID=2#null.
- The mechanic reported to the captain "Yes, de-icing finished". During the engine startup procedure the captain asked "And they've got it good and clean under the wings?" The answer was "Yes, there was a lot of ice and snow, now it's fine. it's perfect now". This part of the conversation between the captain and the mechanic ended with the captain saying: "That sounds fine, then, thanks".
- While the aircraft was being de-iced the pilots carried out a routine run-through of, among other things, the departure procedure from Stockholm/Arlanda. During this the captain mentioned, regarding the procedure for engine failure "Engine failure follow ... 2000 ... that's very general".
- After engine startup the captain taxied the aircraft to runway 08. The engine de-icing systems were 'on' for both engines and there was no indication of malfunction in the systems. While taxiing out the captain initially steered the aircraft somewhat to the side of a strip of slush, which was finally crossed at low speed. The average speed during the taxiing, which took approx. two and a half minutes, was 15 kts (28 kph). The captain made a rolling take-off which up until the rotation went normally. The Auto Throttle System (ATS) was engaged.
- The captain started to rotate the aircraft at 0847.07 hrs. Three passengers have said that they saw ice coming off the upper side of the wings as the aircraft took off. At the same time the captain heard an abnormal noise which he could not identify. The sound was recorded by the Cockpit Voice Recorder (CVR) as a low hum.
- After about 25 seconds, flight bangs, vibrations and jerks were perceived in the aircraft. The jerks were experienced as repeated heavy braking.
- The pilots realised that engine malfunctions had developed and, using the engine instruments, traced the malfunctions to the right engine. The first officer said " ... think it's a compressor stall". The captain has stated that - because of the vibrations and the rapid changes in the digital presentation - he had difficulty in reading the engine instruments. He reduced right throttle somewhat, but without the malfunction ceasing. The throttling-down was recorded as a reduction from 1.904 EPR to 1.870 EPR. Altitude was then approx. 2,000 ft (600 m) and 43 seconds had passed since commencement of rotation.
- It can be seen from the aircraft's flight recorder that engine surges had occurred. In the right engine the first surge was recorded 25 seconds after rotation. The aircraft was then at 1,124 ft (343 m) and in cloud. The autopilot was not switched on. According to the flight recorders, throttle control simultaneously changed to an automatic mode which increased throttle setting with altitude. This was indicated discreetly on the instrument panel but not noticed by the pilots.
- In the left engine the first surge was recorded 64 seconds after rotation. The pilots never realised that the left engine was surging.
- An attempt to switch on the autopilot at an altitude of 2,616 ft (797 m) failed and activated the voice warning "Autopilot". The warning continued for the rest of the flight.
- The right engine failed 51 seconds after the first engine surge had been recorded. The left engine failed two seconds later, 78 seconds after rotation. The aircraft's indicated speed was then 196 kts (363 kph) and indicated altitude 3,206 ft (977 m). Shortly after this the aircraft reached its greatest indicated altitude 3,318 ft (1,011 m).
- Slightly later the two EFIS display screens in front of the captain went dead. He made no attempt to recover the EFIS presentation so during the rest of the flight had to rely on a smaller backup instrument for his flight attitude information.
- The first officer has stated that it was only when the engines stopped that he noted the warning indications from the engine instruments and saw that the outlet temperatures were over 800°C. Thirteen seconds after all thrust had ceased, fire warning was given for the left engine. The first officer then activated the fire extinguishing system for that engine. Grey smoke was noticed in the forward part of the aircraft. Fire warning ceased after 26 seconds.
- The air hostess sitting in the cabin rear jump seat was informed by a flight captain traveling privately that the right engine was surging. She tried unsuccessfully to contact the aircraft's captain on the intercom to notify him. She then got the message to the purser who passed it on to the captain.
- A uniformed SAS captain in seat 2C realised that the crew were having problems. He hurried to the cockpit and asked if he could be of any help. The first officer gave him the emergency/malfunction checklist and the captain instructed him to start the auxiliary power unit (APU). The assisting captain's voice was first recorded two minutes and two seconds after rotation when he said "Look straight ahead". He then urged the captain several times to "look straight ahead".
- Once the engines had lost all thrust the crew prepared for emergency landing. The captain began to glide the aircraft in a gentle left turn which was interrupted on an approximately northerly heading. At the same time the first officer notified Stockholm control that there were engine problems and asked to return to Stockholm/ Arlanda. The air traffic controller ordered a right tum to bring the aircraft back for landing at Stockholm/Arlanda (runway 01). The captain continued, however, the northerly glide. The captain called several times "Prepare for On Ground Emergency". The order was passed aft once by the assisting captain. The purser made a complete announcement over the PA system in accordance with the notification.
- When the aircraft was approx. 420 m above the ground and still in cloud the assisting captain started gradually extending the flaps. According to the flight recorders, speed was then approx. 165 kts. The flaps were fully extended approx. 30 seconds later at a height of approx. 300 m above the ground. At a height of approx 340 m (1,100 ft) above the ground the captain said: "Flaps eh ... eh", whereupon the assisting captain answered: "Yes, we have flaps, we have flaps, look straight ahead, look straight ahead!"
- When the aircraft was entirely free of the cloud at 300 to 250 m (980 to 820 ft), the captain judged that a large field far to the right could not be reached. Instead he chose to attempt an emergency landing in a field more or less in his direction of flight, north-east of Stockholm/Arlanda. During the approach to the field the captain corrected his heading about 25 ° to the right to avoid houses further on in the intended direction of landing.
- Seventeen seconds before the aircraft struck the ground the first officer asked "Shall we get the wheels down?" This was answered by the assisting captain with the call: "Yes, gear down, gear down." Eight seconds later, when height was 56 m, the first officer reported to Stockholm control: "and Stockholm SK 751 we are crashing to the ground now." A further seven seconds later the sound of contact with trees was recorded on the CVR.
- According to the flight recorders the landing gear was extended and locked at about the same time as the aircraft hit the first trees. The speed had then decreased to 121 kts. The major part of the right wing was torn off and the aircraft began to bank right. The last flight recording one second before impact was 107 kts, with a 19.7 ° right bank.
- Four minutes and seven seconds after rotation the aircraft hit sloping ground, first with the tail. On impact, a right bank of 40.1 ° was recorded. After impact the aircraft slid along the ground about 110 m before stopping. The fuselage was broken into three on impact and during the subsequent braking along the ground. There was no fire. All 129 on board survived. Except for four persons, all made their way out of the aircraft themselves.