Update #1: preliminary info from the TSB on lightning, touchdown point, and thrust reversers

Update #2: Environment Canada noticed the crosswind as well

Other aviation bloggers have posted sensible things about yesterday’s accident at Pearson, mainly slapping down the media and (even worse) retired pilots and other aviation experts who should know better than to speculate wildly. Like everyone else, I was glued to the TV and Internet, hoping, but not daring to believe that anyone — much less everyone — could have survived.

Still, while speculation is a bad thing, neutral information is not. Since the Canadian TSB does not publish preliminary reports, I thought it would be worth publishing what factual information I can find.

METAR

I downloaded the 19Z, 20Z, and 21Z METAR cycles from ftp://weather.noaa.gov/data/observations/metar/cycles/. The 19Z cycle had a single METAR report for CYYZ:

CYYZ 021900Z 22007KT 4SM +TSRA BKN050TCU BKN080 24/23 A3003 RMK TCU6AC1 CB ASOCTD SLP168

The 20Z cycle had a whole series of METAR reports, mostly within a few minutes of the accident (which occurred at 20:03Z):

CYYZ 022004Z 34024G33KT 1 1/4SM +TSRA SCT015 OVC045TCU RMK RA2SF2TCU5 CB ASOCTD

CYYZ 022000Z 29011KT 4SM +TSRA BKN051TCU BKN140 23/22 A3002 RMK TCU6AC1 CB ASOCTD LTGCC VIS LWR SW-NW 2 SLP164

CYYZ 022004Z CCA 34024G33KT 1 1/4SM +TSRA SCT015 OVC045TCU 23/ RMK RA2SF2TCU5 CB ASOCTD

CYYZ 022004Z 34024G33KT 1 1/4SM +TSRA SCT015 OVC045TCU RMK RA2SF2TCU5 CB ASOCTD

CYYZ 022004Z CCA 34024G33KT 1 1/4SM +TSRA SCT015 OVC045TCU 23/ RMK RA2SF2TCU5 CB ASOCTD

CYYZ 022020Z 34024G33KT 3SM +TSRA FEW015 OVC040TCU 23/ RMK SF2TCU6 CB ASOCTD

All the reports agree that the wind was from 340° true (350° magnetic) at 24 knots gusting to 33 knots. Visibility at the time of the accident was 1 1/4 statute miles, improving to 3 statute miles by 20:20Z. Ceiling was 4,500 feet AGL, lowering to 4,000 feet AGL by 20:20Z. All report severe thunderstorms and rain, with towering cumulus and cumulonimbus cloud associated. The temperature was 23° celsius, and the dewpoint was the same or very close. (Update: Environment Canada has mentioned the crosswind.)

The 21Z cycle had just one METAR, again, for CYYZ:

CYYZ 022100Z 18013KT 8SM -TSRA BKN055 BKN140 22/19 A3004 RERA RMK SC5AC2 CB ASOCTD FU ALF SLP171

By 21Z, the wind had diminished and backed to 180° true and visibility had improved, but there was still thunderstorm activity. Note in the remarks “FU ALF” (smoke aloft), likely referring to the smoke from the burning plane.

Runway and Approach

According to the Canada Air Pilot, the ILS/DME 24L approach at CYYZ has a decision height of 250 feet AGL (797 feet MSL) with an advisory visibility of 1 statute mile or runway visual range (RVR) of 5,000 feet. The runway heading is 237° magnetic, or 227° true. Relying solely on the METAR, which includes observations take some distance from the runway threshold, the flight landed with a tailwind of between 8 and 11 knots and a crosswind of between 23 and 31 knots.

Update #1: Friday 5 August

On Friday 5 August, Real Levasseur, the lead investigator for the accident from the Transportation Safety Board, shared some preliminary information with the press:

• There is no evidence that the plane was struck by lightning.
• The plane touched down further down the runway than usual, at least for that aircraft type.
• The thrust reversers were working properly.

Note that information from the flight data and cockpit voice recorders were not yet available to Lavasseur at the time of the press conference.