|Title:||Aircraft incident to SE-KPE during approach to the Malmö/Sturup airport, M county, Sweden, on 03 December 1999|
|Micro summary:||On approach, this Saab 340 was hit by lightning, causing dual generator electrical failure.|
|Event Time:||1999-12-03 at 1701 UTC|
|Publishing Agency:||Swedish Accident Investigation Board (AIB)|
|Report number:||RL 2000:32e|
|Site of event:||Approx. 17 km. north of the Malmö/Sturup airport|
|Departure:||Örebro Airport, Sweden|
|Destination:||Malmö/Sturup Airport, Sweden|
|Airplane Type(s):||Saab SF340A|
|Type of flight:||Revenue|
|Executive Summary:||Skyways flight JZ 965 was on a regular flight between the Örebro and Malmö/Sturup airports on the 03 December 1999. The commander was the flying pilot for the leg and the flight experienced moderate turbulence. Lightning had been reported by other aircraft in the Malmö area but the crew was unable to see any storm activity on their weather radar.|
After the crew had received clearance to commence an ILS1 approach to runway 17 at Sturup and was established inbound on the LLZ2, the aircraft was hit by lightning, causing both engine driven electrical generators to trip off. The aircraft was at an altitude of 2700 ft. approximately, and 9 nautical miles from the runway. All instruments except for the standby flight instruments and the emergency lighting ceased to function and the crew was unable to communicate with Air Traffic Control (ATC).
The crew continued the approach using the standby instruments while trying to reset the generators by cycling the switches from ON to OFF-RESET and then back to ON, with no success. By using a similar procedure with the radio they were however able to re-establish contact with ATC, and informing them of the difficulties they were experiencing and ask for radar vectors during the approach. The commander decided to continue the approach using the standby instruments and land as soon as possible after making some small turns to see that they were indeed indicating properly and giving correct information.
When extending the landing gear the crew was unable to get three green down-and-locked indications, even though the lamps tested correctly. They tried to retract and extend the gear several times, but the result was the same. It was first when the emergency gear extension procedure was used that the crew was able to get three green safe indications. The flight was at this point at 2000 ft. established on the ILS.
The air traffic controller asked the flight if they were declaring an emergency, which the crew confirmed. The controller then alerted all the concerned parties as outlined in their instruction booklet “Green Checklist- Risk for Accident”.
When the aircraft was struck by lightning the cabin had already been prepared for landing and the cabin attendant was seated with her seat belt fastened at her station. She contacted the pilots and received information about what had happened and that the flight would shortly be landing. This information was then passed on to the passengers.
The pilots made visual contact with the runway at a height of about 1000 ft. and carried out an uneventful landing. After landing they were finally able to reset both engine driven generators. All instruments began to then function normally except for the EFIS3 screens, which had a somewhat paler colour scheme. After having reached their parking stand the commander informed the passengers about what had happened and made sure that no one had been injured.
A visual inspection of the aircraft showed a 40–50 cm long crack in the upper part of the nose radome.
The aircraft type is equipped with two independent electrical systems, each consisting of a generator and a battery, with each generator having automatic overvoltage protection. The two systems are normally connected through a Bus Tie Relay, which opens and disconnects the two systems from each other automatically should an electrical fault arise in one of the systems, thus protecting the remaining and intact system. The first action in the malfunction checklist for the loss of both generators is to manually open the Bus Tie Relay.
Lightning strikes have on earlier occasions caused the overvoltage protectors to automatically disconnect both generators on this aircraft type. Experience has shown that the generators can be reset to ON after a period of about 15 seconds. The aircraft manufacturer is producing a modification that will reduce the risk for unnecessary generator disconnects.
After the incident the landing gear system was found to be without fault. No proper explanation has been found to explain why the crew did not get a correct down-and-locked green indication during the first attempts to extend the gear. The aircraft is equipped with an electrical hydraulic pump that is normally driven through power from the generators.
|Learning Keywords:||Operations - Lightning|
|Systems - Electrical|
|Systems - Flight Instruments|
|Consequence - Damage - Airframe or fuselage|
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