Table: tupolev tu - 154
Question: Have there been any incidents involving the Tupolev TU-154 where the cause of the accident was not immediately clear? Answer with only 'Yes' or 'No' that is most accurate and nothing else.
Step 1 (Reasoning, Other Commonsense Reasoning): immediately clear
Step 2 (Reasoning, Grounding): cause of the accident, brief description
Step 3 (Operation, Indexing): brief description
Step 4 (Reasoning, Reasoning with Quantifiers): existential, any incidents
Answer: No