Why was the 1987 attempt successful, and Yousef's a failure? Probably because the North Koreans used much more powerful explosives: about 350 grams of C-4 plastic explosive (concealed in a radio) and about 700 milliliters of liquid PLX explosive (concealed in a liquor bottle). The C-4 was presumably a booster used to detonate the somewhat less sensitive main charge of PLX. The PLX alone was powerful enough to do catastrophic damage to an airframe. Check out this Youtube video showing the effects of 700 mls of PLX attached to a tree trunk.
According to documents found on Yousef's computer and presented in evidence at his trial (here's a PDF version), he had planned to use bottles of contact lens solution filled with nitroglycerin, plus Casio digital watches as timers and two 9-volt batteries as a power source. Assuming he used about the same in his trial run, his explosive charge just wasn't big enough to ensure destruction of an airliner in flight.
Yousef's thinking was way ahead of the curve in one respect. The 9/11 Commission's report said that he also had prepared dolls wearing clothes containing nitrocellulose, an explosive compound. Explosive-bearing clothing would really raise the stakes for airport security screening; presumably, it would mandate that everything going on board first be screened with an explosives trace detector. So the next time you're at an airport and (like me) you're cursing the take-off-your-shoes-and-belt procedure, just be thankful that you're allowed to wear clothes at all.
1984 (Portugal) – The U.S. embassy was struck by four mortar rounds fired by the 25 April Movement. The Movement, a Marxist group, was commemorating the ninth anniversary of a failed coup attempt by the Portuguese Communist Party against the military government. There was no significant damage to the embassy.
2000 (Israel/Syria/Lebanon) – A Hezbollah bomb attack killed one Israeli solider and wounded two others near Shaba Farms. The Farms are a small disputed area located at the junction of Israel, Syria and Lebanon, consisting of 14 farms on 10 square kilometers. Israel withdrew from the area in May of 2000 in accordance with UN Resolution 425, and the final status of the territory remains to be settled by negotiations between Israel and Syria (according to the UN, which determined in 2000 that the Farms belong to Syria). Hezbollah has kept the land status in dispute by pressing a Lebanese claim to the Farms, and therefore retains a pretext to attack Israel.
1975 (United Kingdom) – BBC television presenter Ross McWhirter, an outspoken critic of the IRA, was shot to death outside his London home shortly after he had offered a reward for information leading to the arrest of IRA bombers. The IRA unit that killed McWhirter, and had also carried out dozens of other attacks in London throughout 1975, was arrested two weeks later after a six-day siege of their barricaded flat. Hugh Doherty, Martin O'Connell, Eddie Butler and Harry Duggan were charged with 10 murders and 20 bombings and jailed for life in February 1977. They were freed in April 1999 under the terms of the 1998 Good Friday Agreement that ended the conflict in Northern Ireland.
2002 (Kenya) – An Israeli Arkia charter airliner leaving Mombassa’s airport and a resort hotel occupied largely by Israeli vacationers were attacked simultaneously by al-Qaeda. The airliner, carrying 261 passengers, was evidently targeted with two shoulder-fired surface-to-air missiles shortly after takeoff, but was undamaged and continued to Israel. Ten minutes later, a jeep was driven into the lobby of the Paradise Hotel and detonated in a suicide-bomb attack, killing 13 employees and two guests. When the airliner’s Captain realized the plane had been attacked he opted not to make an emergency landing, and flew 2,000 miles directly to Israel.
1987 (Andaman Sea near Burma) – Korea Air flight 858 exploded over the Andaman Sea while en route to Bangkok via Baghdad and Abu Dhabi. All 115 persons aboard were killed. Officials in the United Arab Emirates and in South Korea quickly identified two suspects in the bombing, a man and a woman who had quickly deplaned from KA 858 in Abu Dhabi and then immediately transited to Bahrain. When authorities in Bahrain detained them, both bit into cyanide capsules that had been concealed inside cigarettes.
Kim Sung Il, age 70, died almost instantly, but the other agent, 26-year-old Kim Hyon Hui, survived and was extradited to South Korea. In January, 1988, Ms. Kim announced at a press conference that both she and her partner were North Korean agents, and said that they had left two explosive devices in an overhead luggage rack.
1989 (Germany) –Alfred Herrhausen, President of the Deutsche Bank, was assassinated by the Red Army Faction (RAF) shortly after leaving his home. He was being chauffeured to work in his armored Mercedes, with bodyguards in both lead and follow vehicles, when the RAF triggered an innovative roadside bomb that fired a 20 kilo (44 pound) explosive charge hidden in a school bag on a bike parked next to the road that Herrhausen would travel. The bomb’s trigger was connected to a light-activated switch that was tripped when Herrhausen’s limo broke the beam of light. The bomb was carefully located so that the blast could be focused on the car’s rear passenger area where Herrhausen was sitting.
In September, 1999, Austrian police killed RAF member Horst Ludwig-Mayer and arrested his accomplice, Andrea Klump, who had evidently been involved in the Herrhausen ambush. Klump faced charges in connection with that and other RAF attacks, including one against a NATO installation in Spain in 1988, and the bombing of a train in Hungary that carried Jewish refugees from the USSR en route to Israel under the terms of the Jackson-Vanik Agreement.
On trial in Germany, Andrea Klump confessed to the attempted bombing in Spain and was sentenced to nine years in prison. Klump also confessed to involvement in the 1991 Hungary bombing, stating that she was aware of the operation prior to its execution but denied direct involvement in it. However, police found DNA evidence that Klump had stayed in Budapest around the time of the bombing, and in 2004 Klump was sentenced by a court in Stuttgart to a further 12 years in prison.
2001 (Israel) – Two HAMAS suicide bombers detonated explosives in a shopping mall, killing eleven persons and wounding 120. This double suicide bombing occurred at the Ben-Yehuda pedestrian mall in Jerusalem at 11:30 PM on a Saturday night, a peak hour for traffic in the area. The Ben-Yehuda mall is a popular area filled with shops, bars and cafes, so the timing of the attack maximized the number of casualties.