Stall and Fatal Crash at Houston Hobby
On the 9th of June 2016, a Cirrus SR20, registration N4252G crashed during a go-around at William P. Hobby airport, killing the pilot and two passengers.
I first heard of this accident as a result of the AOPA Air Safety Institute’s video series although it happened a few years ago. I recommend the video but of course I wanted to get in deeper and try to understand better what happened. This is based on the NTSB Report CEN16FA211 and the ATC group report in the NTSB docket, both of which are available on the on the NTSB website.
The pilot had completed her PPL just over two years before, in 2014. The FAA requires a flight review every 24 months and hers was a month over due, however everything else was in order.
She planned the flight to Houston’s William P. Hobby Airport (HOU), Houston’s oldest commercial airport. She had two passengers on board, her husband and her brother-in-law. As HOU is just seven miles from downtown Houston, it was the closest airport for them to visit a family member who was undergoing cancer treatment at a local hospital.
This was probably her first trip to Houston Hobby Airport, a high traffic airport and a hub for Southwest Airlines. According to her log book, she had landed in Class B airspace four times, most recently with a landing and take-off at Dallas Love Field in Texas the week before.
On that day, the pilot and two passengers departed Oklahoma Westheimer airport at 10:11 local time and flew south to Houston. She contacted Houston Approach with the current ATIS information and was told to descend to 5,000 feet and maintain VFR. The flight received routine VFR handling and after descending to 1,800 feet, the approach controller told the flight to expect a left base to the traffic pattern for runway 4.
HOU Approach: You’re following a Boeing 737 about one o’clock and five miles…on a four mile final at 2,000. Caution for wake turbulence.
This is informational: the Boeing 737 is on approach and the Cirrus SR20 should make visual contact and be careful not to approach too closely, as the wake turbulence from the larger aircraft could be dangerous for the Cirrus. The strength of the wake turbulence is governed by the weight, speed and wingspan of the generating aircraft, in this case the Boeing 737. Aircraft are put into categories determined by their gross weight (although technically the best classification system would be wingspan) with minimum wake-turbulence separation distances established based on the categories of the leading and the following aircraft.
The pilot confirmed that she had the other aircraft in sight. The approach controller instructed the pilot to fly a heading of 095° in order to shorten the approach and then asked her to change frequency to Houston Hobby Tower. He then asked the Boeing 737 to reduce its speed and then also to change frequency to Tower. He continued to monitor their spacing.
At 12:52, the pilot contacted Houston Hobby Tower. At that time, the station was manned by a trainee with an instructor. “Tower” or “local control” is the air traffic control station responsible for active runway surfaces: they clear aircraft for take-off and landing, ensuring that separation is maintained at all times. Tower control works with Approach and with Ground in order to maximise traffic flow and ensure spacing between inbound and outbound aircraft. If the Tower controller detects any unsafe conditions, they may instruct a landing aircraft to go around and then be re-sequenced, which could mean transferring the aircraft back to Approach to circle around and start again.
The Cirrus SR20 pilot identified herself as N4252G and inbound to land. The trainee misunderstood the pilot’s initial contact and thought that the call came from an inbound 737, Southwest Airlines flight 235, which he cleared to land. Once the instructor pointed out the confusion, the trainee called back to clarify.
Trainee Controller: Cirrus 4252G, Hobby Tower. You’re number 2 following a 737 on a 3 mile final, caution wake turbulence. Runway 4 cleared to land.”
This made Southwest Airlines flight 235, who called in next, number three to land. It was clearly busy but nothing out of the ordinary for Houston Hobby airport.
The Cirrus pilot read back the instruction, at which point the trainee asked where she would be parking.
Cirrus N4252G: We’ll be parking at MillionAir.
Trainee Controller: Cirrus 4252G proceed direct to the numbers, you’re going to be inside a 737 intercepting a 10-mile final.
Proceed direct to the numbers is a reference to the threshold numbers on the runway: instead of following the rectangular pattern known as a circuit, the pilot should fly directly to the threshold of the runway ready for landing. This is common for light aircraft at large US airports, where there isn’t a lot of point in a single engine plane following the same pattern as a massive twinjet airliner. The request is most commonly used to try to get a slower aircraft to land and clear the runway quickly so that it is out of the way of an inbound jet. At the same time, ATC shortened the call sign for the Cirrus to N52G for faster reference. I will do the same.
Cirrus N52G: OK, you’d like me to proceed direct to the numbers, 4252G?
Trainee Controller: November 52G, what did approach tell you before?
Cirrus N52G: Um, to left base runway 4 and follow the Boeing.
Trainee Controller: …proceed direct the numbers for runway 4, direct to Hobby.
Meanwhile, the approach controller who handed her over to tower was working five or six other aircraft but he noticed that the Cirrus was still heading toward the outer marker, that is, still following the rectangular pattern rather than cutting the corner to the runway. He called the tower to ask them to turn the aircraft directly to the runway. He also wanted the Cirrus out of the way of the much faster Boeing 737, which was gaining on her. If the Cirrus didn’t land quickly, Southwest Airlines flight 235 would have to go around and approach again.
Tower staff confirmed that they’d already done this and the trainee contacted the Cirrus again. He instructed her to maintain maximum forward speed and proceed direct to the numbers, explaining that there was a Boeing 737 on 9-mile final following her and 80 knots faster than her.
Clearly this was to put the pressure on for her to get a move on, but the pilot remained calm, responding that she would proceed direct to the numbers and keep her speed up.
The trainee controller then broadcast to all aircraft that the ATIS (automatic terminal information service) had updated to information India. This is a small thing and there was no need to acknowledge, but for a pilot with not a lot of experience at major commercial airports, it seems clear that things were starting to pile on.
Southwest Airlines flight 235 contacted Houston Hobby to say they were on five mile final for runway 4. The trainee controller responded that Southwest was number two following a Cirrus on two-mile final, clearing the flight to land and asking him to slow to final approach speed.
The trainee controller then broadcast a wind check: 080° at 13 knots gusting to 18 knots. The wind was blowing down runway 4, perfect for landing.
The Tower instructor and the trainee discussed whether the spacing would work as the spacing between the Cirrus and the Boeing 737 behind it was decreasing. The instructor knew that runway 35 was also available for landing and so rather than send the Cirrus back out to approach for re-sequencing, he thought it would be better for the pilot to go around and use runway 35 instead. Rather than leave it to the trainee, he called the Cirrus himself.
Tower Instructor: Yeah, I’ve got traffic behind you, just go around and fly runway heading for now, maintain VFR, and I’m going to put you back on the downwind for runway 35. The winds are 090 at 13 gusting 18. Can you accept runway 35?
Cirrus N52G: We’re to go around and line up for runway 35 downwind.
The instructor instructed the pilot to go ahead and fly runway heading 4 for now, that is, carry on straight long the runway, with the implication that she she shouldn’t worry about setting up for the runway 35 approach yet. The Cirrus pilot read the instruction back and, with the Cirrus safely out of the way, the instructor cleared Southwest flight 235 to land.
Tower Instructor: N52G, when able, go ahead and make a right downwind turn now for runway 35 and then we’ll just go ahead and keep that right turn, runway 35 cleared to land.
Cirrus N52G: OK, make a right downwind for runway 35?
Tower Instructor: N52G, yes, and just keep the right turn all the way around, you’re just going to roll right into the base for runway 35, cleared to land. I’ve got another 737 on five-mile final to runway 4 and you are going to be in front of him.
Cirrus N52G: turning around for runway 35.
Tower Instructor: Just enter the downwind for runway 35.
I’m pretty sure I’d be stressed out trying to follow these instructions, knowing that now another Boeing 737 was bearing down at me, but the pilot continued to respond calmly. The Tower controller told her that he would call the right base turn. Effectively, he’s planning to get the Cirrus down on runway 35 through a gap between the arrivals on runway 4.
At this point, the trainee controller took over and contacted the pilot with a traffic advisory: another Boeing 737 inbound to runway 4. The pilot confirmed she had the 737 in sight. The trainee controller then instructed the pilot to make a right base turn to follow (in this context meaning pass behind) the 737 and again cleared the pilot to land on runway 35.
Cirrus N52G: We’re going to make a right base following them…for runway 35, N4252G.
The instructor, watching on radar, realised that the Cirrus was overshooting and not properly lined up for runway 35. He became concerned about loss of separation with Southwest flight 235 which was coming in to land on runway 4.
The trainee controller told the pilot to turn left heading 30°, in order to resolve the possible conflict. It’s not clear if the controller meant that the Cirrus should turn left by 30° or to turn to a heading of 30°. The pilot read back the instruction but this time, she didn’t sound confident about what she was expected to do. The Tower Instructor took over and offered a new plan; he asked if the pilot would prefer to follow the 737 to runway 4.
Cirrus N52G: Yes, that would be great.
Note that’s a shift from runway 4 to runway 35 and then back to runway 4, all in less than two minutes. The pilot sounded like she was coping but this is definitely adding to overload in a busy airport during an already stressful phase of flight.
Cirrus N52G: Am I turning a right base now?
Tower Instructor: Roger, just maneuver back for the straight-in, I don’t know which way you’re going now, so just turn back around to runway 35.
Now, I’m sitting comfortably at a desk reading a transcript and I had to read that twice to understand that the controller had changed his mind, presumably as she didn’t react clearly enough, and was now asking her to line up for runway 35 again, this time for a straight-in, although he wasn’t clear what she was doing at that moment… while Boeing 737s seem to be flying all around her.
Cirrus N52G: Turning to 35, I’m so sorry for the confusion.
Tower Instructor: That’s OK, we’ll get it.
I need to say here, the confusion was not her fault. She’d perhaps misunderstood quite how to follow the 737 into runway 4 but she had been repeating and following instructions throughout. Meanwhile, the controllers seemed to treat her like a pinball, to be batted out of the way while they deal with the bigger aircraft.
About 30 seconds later, the Instructor asked the pilot which direction she was turning.
Cirrus N52G: I thought I was turning a right base for 35.
Tower Instructor: That’s fine, uh, just make it, uh, you say you’re in a right turn, keep it tight, I need you to make it tight.
Cirrus N52G: Keep turn tight.
The controller then gave a general aviation traffic alert for traffic one mile away at 900 feet, referring to the Cirrus. Another aircraft reported that he was looking.
Tower Instructor: N52G, I need you to …there you go, straight in to runway 35, cleared to land.
Pilot: Straight in to runway 35 and I don’t believe I’m lined up for that.
This was the first time the pilot pushed back. The instructor acknowledged this by gave her a completely new instruction.
Tower Instructor: Turn to the right and climb and maintain 1,600, right turn.
Then, having broken off the approach, the controller tried again.
Tower Instructor: OK, 52G, let’s do this. Can you do a right turn back to join the straight-in to 35? Could you do it like that?
Cirrus N52G: Yes, right turn back to 35, N4252G.
He instructed the pilot to make a right turn all the way around to runway 35 and again cleared the pilot to land.
At the same time, the approach controller called the Tower to offer a space to put the Cirrus behind another aircraft, N4JJ, which was inbound and on final for runway 4. He got no response.
N4JJ contacted the tower on a visual approach to runway 4. The Tower Instructor told the pilot to reduce to minimum speed, advising that he would be number two for the airport, following a Cirrus on one-mile final for runway 35, which the pilot of N4JJ acknowledged.
Tower Instructor: Cirrus 52G, OK, you’re looking good. Just continue a right turn for runway 35. Do you see runway 35 still?
Cirrus N52G: Yes, 35, have it in sight, continuing my roll around.
Tower Instructor: Yes, ma’am, yeah, you’re good so you can start your descent to runway 35 there, and uh, cleared to land on 35.”
Cirrus N52G: Cleared to land on 35, thank you very much.
Tower Instructor: …winds are 100 at 15 gusts to 20 [knots]
Cirrus N52G: OK, thank you. Trying to lose altitude.
Tower Instructor: No problem, little bit of wind off the right.
Tower Instructor: N52G, if you don’t want to land — if that’s too high, we can put you back around the downwind, don’t force it if you can’t.
Cirrus N52G: OK — we’ll see, thank you.
Tower Instructor: OK, I think you’re too high, Cirrus 52G, you might be too high.
Cirrus N52G: OK, we’ll go around then, N4252G.
The Tower Instructor told the pilot to make right traffic for runway 35. This means to join the right-hand circuit for runway 35 and the pilot responded that it sounded perfect and repeated the instruction.
As the Cirrus continued along the right-hand circuit, the Tower Instructor once again cleared the Cirrus to land.
Tower Instructor: …make right downwind to runway 35 and you are cleared to land. There will be no other traffic for runway 4 so this one will be easy.
His words were at least an acknowledgement that it had not been easy so far. I know I might be projecting, as it’s easy to imagine myself in the position of the low-hours pilot trying to deal with a busy commercial airport in what was probably her first visit, so she was unlikely to really know the area or the patterns beyond looking at the charts that morning. It is all-to-easy to put myself in her place and feel the tension increasing.
Cirrus N52G: Making right traffic for downwind for runway 35.
Tower Instructor: Affirmative and cleared to land on runway 35 via the right downwind and right base.
Cirrus N52G: Thank you — right downwind, right base.
Tower Instructor: There’s a 737 on short final runway 4 touching down right in front of you so just caution wake turbulence right there at that intersection.
Cirrus N52G: OK, I’ve got that in sight.
The instructor controller asked if the pilot had the runway in sight and once she replied that she did, he provided a wind check. Landing on runway 35 meant landing into a bit of a crosswind but no one seemed bothered by this.
The Tower’s front line manager contacted approach and asked them to slow their next arrival down, in order to build a little more space for the Cirrus. However, final approach was “pretty full” up to about 20 nautical miles and the next aircraft was already at the final approach fix, so approach could not slow down the inbound aircraft. The approach controller thought that the Cirrus was landing on runway 4 and didn’t think that the Tower could get the Cirrus down before the next aircraft, so he offered to take the Cirrus back, effectively pulling her out of the pattern for a new approach. As the pilot was already turning base for runway 35, the front line manager replied that Tower would continue with the aircraft. The approach controller didn’t realise that the Cirrus was landing on runway 35 until she turned final.
Still sounding confident and collected, she acknowledged that she was too high once again. The Tower Instructor said later that having an aircraft miss the runway twice was very unusual but that as the aircraft was VFR, that is, flying visually, keeping it in the pattern was the normal response. It never occurred to him to transfer her back to Approach to start over.
At this point, there was a shift change. The trainee was asked to relieve the ground controller so that he could take over the local control from the instructor.
Cirrus N52G: Going around, third time will be a charm.
The new controller was relieved to see the Cirrus go around because it looked high and he was concerned that she wouldn’t touch down until the end of the runway. He said later that she sounded composed and in control as she prepared for another approach.
Tower Instructor: OK, Cirrus 52G, just go ahead and make the left turn now to enter the downwind, midfield downwind for runway 4. If you can just keep it in a nice tight low pattern, I’m going to have traffic four miles behind you, so I need you to just kind of keep it in tight if you could.
Cirrus N52G: OK, this time will be runway 4, turning left.
The controller’s plan was to have the Cirrus follow a 737 on final to runway 4 but he was also considering taking her to runway 35, depending on traffic.
Tower Controller: And actually, I might end up sequencing you behind that traffic, he’s on four miles a minute…um, it is going to be a bit tight with the one behind, so when you get on the downwind, stay on the downwind and advise me when you have that 737 in sight. We’ll either do [runway] 4 or we might swing you around to 35, uh…
He stopped as he saw the aircraft winging over and “going steep.”
Tower Controller: Ma’am, ma’am, straighten up. Straighten up!
He never received a response. The Cirrus crashed into a parking lot northwest of the airport at 13:08.
Putting the whole thing together, here’s the ground track of the flight over the course 15 minutes, from the time she contacted Tower:
The pilot of the Cirrus had become so overloaded, she’d lost track of the airspeed of the aircraft. She became completely focused on following the latest instruction (or non-instruction, while the controller thought out loud about what he was considering) that she never even thought about the risk of a stall. As she turned away from runway 35, she retracted the flaps ready to turn and line up for another approach on runway 4… but it was too soon. When breaking off an approach, the pilot should have brought the Cirrus to 81-83 knots indicated airspeed before changing the configuration of the aircraft. The Cirrus published stall speed with flaps up is 69 knots. The pilot was only showing 58 knots indicated airspeed when she retracted the flaps.
Th Cirrus SR20, already low and slow, spun to the left. The nose dropped 45° and the Cirrus crashed into a hardware store parking lot. The Cirrus parachute rocket motor activated during the impact, much too late. The impact was not survivable.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot’s improper go-around procedure that did not ensure that the airplane was at a safe airspeed before raising the flaps, which resulted in exceedance of the critical angle of attack and resulted in an accelerated aerodynamic stall and spin into terrain. Contributing to the accident were the initial local controller’s decision to keep the pilot in the traffic pattern, the second local controller’s issuance of an unnecessarily complex clearance during a critical phase of flight. Also contributing was the pilot’s lack of assertiveness.
If you want to hear the original radio and follow the sequence as a video, then I highly recommend the AOPA accident case study.
I’m not crazy about the contributing cause of a lack of assertiveness. The controllers and the pilot were all trying to achieve the same thing: get the Cirrus on the ground. She consistently sounded professional and composed on the radio, which controllers agreed led them to believe that she was confident and in control, but I don’t think you should hold good radiotelephony against a pilot. She could have specifically requested to be re-sequenced — transferring to approach as she flew away from the airport, so that they could bring her in again — but it would again mean fitting the slow Cirrus in between the Boeing 737s with the same issue of the larger planes gaining on her, so she may not have believed there would be any benefit.
Peter Garrison of Flying Magazine makes a further point.
Examining the Aftermath of the June 2016 Crash of a Cirrus SR20
A point that the NTSB does not mention is that a go-around from a full-flap approach is a delicate maneuver that pilots are seldom called upon to perform. A pilot making an instrument approach to minimums avoids using full flap, until landing is assured, for that very reason. It is quite possible that since her training, the pilot of the Cirrus had never had to perform such a go-around, and now, suddenly, she was given not one but three chances to fail.
I’m not saying she had no responsibility. It seems clear that the airport operations required her full attention and thus she lost track of the aircraft’s speed and configuration, reacting to the controllers’ instructions without acknowledging that she was unable to keep up with their demands.
Just, it’s so easy to see myself in this one and struggling on, never quite acknowledging that it has all become too much. It’s not like you can simply pull over and work out what you need to do or even just take a deep breath.
This is a tragic failure but also a classic one. The report covers the detail but what it doesn’t do is highlight points at which a different decision could have changed everything. I’ll leave that to you in the comments.